I'm Norwegian. After using a Colemak based on the standard Norwegian layout with just the relevant letters swapped and the special letters æøå to the right, I ditched that for a more or less standard US Colemak. In part because the national layout was horrible when it came to punctuation placements, and in part because sticking to the standard layout is a distinct advantage. Hotkey helpscreens for complex software, for instance - or poorly implemented software that expect certain keys to be available (such as a tilde that isn't on an AltGr key).

Luckily, I still have my VK_102 key (which I've moved into the middle between Colemak B and K for reasons of ergonomy). That holds the most common of the Norwegian characters (the 'Ø'). The other two are on AltGr and [] - but if I were to use Norwegian a lot more I'd swap the brackets over to the AltGr positions and have two layouts that were almost equal but for the focus on coding vs Norwegian. So I get three special keys to play with, without mucking up the general layout.

The special accent key is in the standard Norwegian layout too. But I did away with that. I think that using AltGr and colon (for diaeresis), 6 (for circumflex), ' (for accent) etc. works more intuitively for me.

All in all, that works very well for me. I know that you have more keys you want to fit in, and you're welcome to use those keys for it. But I'd rather hit the AltGr a bit for the rarer signs, myself.