EPKL can do nearly all of that. I don't know of any other free software that will do composes and everything else you need. It will not work on first startup since it has to run a program, but I don't think you'll get any single software that does absolutely everything you ask for. One answer is a hybrid solution: I use EPKL in conjunction with MSKLC and SharpKeys (registry remapping) for a complete and robust total solution.

Home row mods may be the hardest thing to accommodate. I haven't gotten the timing right or something, so I haven't looked at it for a while. I don't feel the need for them myself, with all my other tricks, so that's a thing.

EPKL, like AHK, in itself doesn't need admin rights, just run rights. It's portable and can be run from a USB drive or even over an internet connection I think. It's not 100% stable but good enough I'd say and easy to refresh by a hotkey. Not robust in all games, as holding down keys for a long time leads to the generation of an overflow of system hotkeys. Also easy to suspend (by hotkey or automatically by app or layout). I've used it with VMs in different ways.

I am EPKL's creator. It is based on PKL by Máté Farkas, and it is compiled AHK code. I am open to suggestions for improvement and additions, but I usually can't promise quick implementations even with sponsoring as it isn't my main job.

See my Big Bag for more info, especially the Windows platform.

If you want a real driver, you may have to pay for KbdEdit. I have no idea whether it's still under active development, but if it is then you may be able to persuade its maker to implement dual-function keys too so you can have your HRMs?

I want to address the issue of hotkey buffer overflow in EPKL soon. In that case, it may become very stable indeed – at least, that's what I'm hoping for. But if and when that'll work is uncertain right now.

HRM: Home-Row Modifier

Good news: EPKL buffer overflow is pretty much fixed already. I don't think it'll hang on you anymore, but of course I cannot be 100% certain as it is a very complex program with much functionality in it. To use the newest EPKL, you have to compile using the enclosed .bat file, from the latest commit. Release versions don't have the latest developments; once the dust settles I'll make a new release but I'm still testing and developing the next release so it's pre-α still.

Other AHK scripts have other issues. I don't use them much but I've heard so. You could harden a simpler AHK script but it'd take a pretty profound knowledge of Windows threads and hotkeys, as I understand it.

I believe EPKL will be more robust, yes. I've worked hard to make it so, as did my predecessor.

Standard AHK scripts may be made more robust by using thread and priority settings right. This is a complex discipline, and I don't fully understand it but often resort to trying out solutions to see how they work.