[MrObvious]

1) I think both pieces of software work. Touchpal for sure works and it seems to be a top SIP amoung us Diamond users along with FingerKeyboard 2.1. I have both and am trying both out and they have their advantages and disadvantages. Personally I like TP a little better because I can text with one hand instead of two but FK2 ater getting used to it for a bit isn't that bad but takes two hands IMO.
2) GPS works fine. Just follow the sticky. As far as tethering it should work with Bluetooth. Just be careful about the 5GB limit or using it too much (don't use it for your primary Internet connection). IDK about bluetooth but I use USB all the time.

That said MightyROM is a good Windows Mobile 6.1 ROM. The only caveat is there is a huge bug where if you use a MP3 ringtone it won't ring after an unknown period of time. For a workaround convert your ringtones to .wav files and put them in \Internal Storage. This seems to be a bug that plagues several ROMs with no known reason why.