Hi Michael -
you're on the right track with the AIS... the baseline is to upgrade your existing VHF to one with AIS reception and display. Most people seem to have settled on Standard Horizon's version of this... current model# is, I think, the GX2200.
What you will want is the model with integrated AIS and GPS. Probably in the neighborhood of $250-300; you'd simply replace the ICOM.
Doubtful that there is a rental solution available that fits the requirements, but I don't know.

Tracker's are a somewhat more personal choice.
The current LongPac rules allow both Iridium Satellite based units (Garmin's (ne DeLorme) various InReach models; Also the Iridium GO!) as well as Spot's units, which use the Globalstar system.
As long as you can send a message from it, you're probably OK.
For my money, I would favor the Iridium units; that's based on the satellite coverage. Iridium is a truly global system... Globalstar is primarily land-centric.
Notably, Spot is unlikely to be accepted for the SHTP for this reason.

DH