1. Don't know, but remember e-tests only apply to cars 20 years and younger, so 86 and earlier are exempt. (not sure exactly what model you're talking about. Literally late model 911, or late model meaning 996/997?)
2. Depends what model, but generally, pretty easy. On my boxster it was a fuse and some wiring, I think $80 parts and labour at Mantis.
3. Any speedo with a digital readout of the speed can be converted - all 996/997/boxster/cayman/cayenne,
AFAIK.
Good luck!