I do believe that you may have the ultimate wheelie machine under construction. That might even merit a wheelie bar.
I considered a lot of the UTV tires until I started comparing their weights. Some of them are 7 ply rated and weigh over 30lbs!!!! In the end, I ordered a Duro HF243. It is pretty old school, but it is only a two ply and weighs less than 16lbs. I didn't want to put a heavy tire on that aluminum rim. I had a 25x12-9 in the shop, so I studded it and was petty happy with the results. The tire I ordered is a 24x11-10. It is coming via USPS, so I'll probably see it in a few months when the sled dog teams make it through the pass.
That is a pic of the 25x12-9.
For the front, I ordered a couple of Carlisle AT489 X/Ls. I think the AT489 IIs would be a great choice but the knobs on the shoulders wouldn't readily handle being studded. The X/Ls have a 3/4" deep lug and should accept a longer stud. I'll get them up and running as soon as the Pony Express arrives.