Good choice. For engine a good alternative is the Edge Performance Rotax – it’s lighter and more powerful. 915 is also fine. Props I’ll leave to someone else.
Is you want to use it as designed – for backcountry flying, you should go for Alaskan Bushwheels. 26″ is actually sufficient, but 29″ looks cool 🙂 (and more draggy) I wouldn’t go bigger than that.
The gear is important for that kind of flying. I use ACME shocks and I definitely recommend them. The Stinger tailwheel is also an excellent choice although somewhat heavier that the stock one (and more expensive) Beringer brakes is also a good choice.
Avionics is personal preference – I would just take whatever Zlin Aviation has as standard.