I going to order the kit from ampedbike.com, but I need to buy 26" tires for it. If anyone out there has one, what width tire do I need to get?

Regardless of what anyone says, you can get away with a wide variety of tires on almost any bicycle rim. If your hubmotor wheel is replacing a 26" wheel that already had a usable tire, that tire is probably fine. If not, I recommend you get a tire between 26x1.5" and26x2.3". If you are sure you would prefer a 26x1.0" or a 26x3.0" tire, that would probably work fine too. The rim (from pictures on goldenmotor.com and ampedbikes.com) looks like it is a very typical MTB rim width.

do not get a tire with a fraction like 26 x 1 3/8, the fraction ones are generally made for a different rim diameter. they are also not very common.

Thanks. The new 26" rim is replacing my 27" rim, so I don't have any old ones, and I'm pretty sure my 27 x 1 1/4 will not fit!