Freerunner

OK, need some advice. I have been reading many of the posts, but unfortunately not black and white for me. I'm 65, last bike I road was 11 years ago and that was a road bike in the Carolinas. Not I live in the mountains in Montana, and the only way I can enjoy the life with my biking friends is to go electric. I tried a friends Specialized Levo SL, which convinced me that electric was what I needed. What was also new to me was the 29". I have been looking at bikes (I know I'll have to wait), and for the 27.5" there is the Kona, Santa Cruz, and Rocky Mountain. For the 29" I see the Specialized Levo Turbo series and Trek Rail series. I do not plan on riding the real hard trails, and will also be doing some roads (out here it's either up or down, no flat roads). I know I want hydraulic brakes and also electronic shifting.
So knowing my riding desires, is there any advantage of 29 vs 27.5? Is this something that I would get used to after riding for a while? Also am I crazy to want electronic shifting on a mountain bike? Welcome any feedback. Thanks