By using auto-hiding panels of quite big size (with adequately sized icons), you can create UI that works finger-friendly, and still leaves 799x479 pixels* for applications.
You might be interested to know (if you don't already know it) that there is an EFL UI for ConnMan called EConnMan but you would need to build it as hasn't yet been packaged for Debian.
I have tried out few browsers. I installed Iceweasel and as you might expect it ate a lot of the memory but other than that there were no real issues and I was able to install some of my favourite add-ons. It's actually quite responsive for single tab/window browsing if you don't have a lot of other stuff running. It runs much better than it does in Maemo under Easy Debian (from what I remember).
I ran into another bug when I tried it in that there was nowhere to enter a URL!
If you want a really lightweight browser then I recommend links2. It does display graphics, just don't expect anything fancy like JavaScript.
This might also be a good option.
I was thinking of something similar. It should be possible to detect whether there's something plugged into the audio jack and automatically switch to the appropriate profile. I'm not actually sure what the critical frequency is. I would very much appreciate it if someone can confirm it.
Hopefully the Neo900 will have protection at hardware level.