On your first question I would 100% advice you to learn proper touch typing. It will increase your speed. I used my own typing technique for a long time and was writing with about 55 wpm or so. Then I decided to learn touch typing (that was still with Qwerty). I took just a few lessons, and since I'm not all that active chatter I raised my speed just to about 60 (and was continuing raising). But after I started type more intensively and switched to Colemak, now I'm writing steadily with 75 wpm for long texts and 85 or so for short (like chat). Often going above 90s.
Anyway, definitely go for touch typing. That's even more important than the layout you're using in my opinion. As for the time it will take you to reach your old speed, it shouldn't be a lot if you go cold turkey, and stop using your non-standard technique, which I advice you to do if possible. But again, either way - it's worth it to learn. If for nothing else - for the comfort you'll feel.

2. I am not 100% sure on what determines the speed limit of a person, but I think everybody reaches a point, after which you most of the times can still improve, but it takes a lot of training, and it's veery slow progress. The technique is important. Just hit three buttons with your index and then hit them with three different fingers. Which is faster? That being said, there are alternative non-classical techniques, but I advice you to go for the classic, and after that if you want, develop your own.
The layout sometimes help the speed, but if you've reached your speed limit with one layout, that's more or less the limit you'll have with the other. The difference is in the stress in the hands and the comfort.

3. I think you're right with the muscle memory. So if your question is which to chose - Colemak or Dvorak, well this is a Colemak forum and I suppose most of the people have made their choice here and will advice you the same. Dvorak is not bad at all, and in some cases better than Colemak but you've probably read the statistics. I wouldn't tell you which to chose. If it wasn't for the shortcuts I don't know which one I would have chosen. I rely veery heavily on shortcuts and Dvorak is just not very friendly on that matter.

PS: The key for good progress and satisfying result is to use exclusively the layout you're learning once you get to a decent speed to do your daily job and as a lot of people in here can tell you - focus on accuracy. The speed comes. Once in the high speeds of typing every mistake costs a ton, so accurate typing is essential if you want to take out the most.

I think you should make the switch. Just testing out colemak for a few days should give you a feel for what its like, and it is a nice feeling!! 

I switched from incorrect qwerty mostly-touch-typing to colemak by testing colemak for an hour in the evenings, and after a few weeks I made the full time switch at work. Thankfully they are understanding and put up with my initial slowness. After a couple of months I outperformed the guy sitting next to me, so I am very pleased :)

Another thing that really got me motivated to make the change was to purchase a new keyboard. I settled on the typematrix (http://typematrix.com) and really like it, but there are plenty of other types too. I got the blank version, so not only is there no text on any of the buttons, anyone trying to use it gets totally lost as its not qwerty either hehehe.

One often overlooked issue though is that software developers are generally using a LOT more symbols than regular english, but this is not really reflected in the usual corpus used when creating layouts (correct me if Im wrong). This tends to put the symbols around the edges of layouts, and often common combos like ); are not considered. I placed the common symbols for my languages in easy to reach places, on the same keys as the common letters, just with a thumb key modifier. Works really nice, the greatest tip I can give is to map the arrow keys to wsad or nuei (in colemak), saves having to move your hand! I love this!

See also the colemak for vim editor, if you use that.

Anyway, in summary, check out colemak, its not too hard to learn, and I at least get a little reward and sense of satisfaction each time I roll out a high speed combo. Great stuff!

Well here's an update nearly 3 weeks later.

I decided to learn DVORAK using the proper touch typing technique and stick with my 2 fingered QWERTY method. I'm trying to stay fluent in both, at least until my DVORAK speed get up to the same as QWERTY. I've got the windows keyboard shortcuts set up to switch back and forth quickly. For browsing the web (passwords, shortcuts, googling) I tend to leave it on QWERTY, as well as for programming as speed isn't an issue and not having to think about how to type what I want is advantageous.

How is the plan going? Well, my QWERTY skills have been doing odd things. I can type normally composing my own thoughts on QWERTY just as fast I always could, but I find it somewhat difficult to take typing tests with it now. I'm unsure if this is because I'm thinking too hard about what I'm typing (this has always happened, if I tried to observe my hands in QWERTY I'd suddenly make all sorts of mistakes and not know where the keys were, versus just typing without really thinking about it) or for some reason my brain just automatically switches to DVORAK when I try typing programs and tests since I've been doing that so much lately. Either way, I'm still able to clock 75WPM+ after enough tries that I start thinking in QWERTY again. I'd say there hasn't been any serious loss of speed or typing ability.

DVORAK with proper typing I made steady progress up to 50-60WPM. At that point, it's leveled off and I seem to have hit a temporary barrier. Part of this might be since I haven't done much typing lately. I will admit that touch typing with the proper form feels more comfortable. It also seems like I'm typing slower than I really am, with less hand movement from both proper form and from DVORAK. In theory, my current DVORAK speed should be fast enough that I can use it easily, but I find that it takes more concentration and thinking to use DVORAK still, making it often frustrating and causing me to switch to QWERTY when I want to type something quickly. At the moment I'm okay with my speed, what I really want is my QWERTY ability to type without thinking, which is harder to measure than words per minute. I'm not really sure how long it will take to regain that.

I really like that: 'multi finger hunt and peck'.  My girlfriend flies with her six finger partially sight read hunt and peck.  I used to be pretty fast myself - but annoyingly never timed myself.  I found it really frustrating moving over to touch typing with the speed loss.

Given hours of stupendous typing, with time and practice you do regain your old speeds - and it starts to feel more natural.  My touch typing doesn't feel as half as rigid as it once did.

It has been a bit of a long climb for me to get to this point.   But don't forget how much time you invested in perfecting multi-fingered hunt and peck!  If I had started out with touch typing though, I think I'd have found it much more comfortable much sooner.

This last week I was forced to use a computer without Dvorak, and my Qwerty talent has totally fallen by the wayside.  I quickly descend into quite a horrible and painful place.

I get where you are coming from regarding pain.  I never had pain or stiffness in my fingers or hand with hunt and peck.  But I did have more trouble with my upper body.

Surely hunt and peck would still lend well to hand alternation - I've always thought that Dvorak would be a better layout for hunt and peckers, for a start it's easier to learn the layout - i.e. less hunting.

@dreymar,  If Colemak had been as ubiquitous as Dvorak - I'd have probably picked that up.  Though I'm glad I didn't. I only have anecdotal evidence as support for Colemak right now - as I'm missing the science bit behind the layout.  You could argue that Dvorak also stands on thin ground - but at least it's tried and tested.  I still think the keyboard is the major problem and challenge to overcome - not so much the layout.

My advice is this! If you feel there is a need to go faster with your current typing speed and if you feel going for proper touch typing will further increase your speed, go for it. Make sure you don’t have any writing assignments for the first two weeks since it will take time getting used to.Does anyone know which is the most preferred landing page software in market?