The shimano 8 speed IGH is apparently very reliable. One doesn't repair them when worn out, one throws them away. I installed a Sturmey Archer S80 IGH, it slowed me down 15% compared to a derailleur and the shifter wore out in 500 miles. I don't think any e-bike has one of those. I expect the 15% drag loss to be the same with the shimano IGH. Don't buy a rohloff 11 speed IGH on an electric bike, there have been leakers.
The 8 speed shimano rear sprocket I have on my yubabike has been very reliable, i've got 5000 miles on it. The 7 speed shimano sprocket axle I had previously came unscrewed and dropped the balls on the road at about 1500 miles. Had to push it home. The 7 speed shimano axle is a kiddie grade product whose main advantage is price. Serious design flaw in that axle, which is on 95% of discount store bikes. Plus I found I was adjusting the shifter on the 7 speed shimano every coupla months, whereas the SRAM shifter on my yubabike needs adjusting less than once a year.
I ride hilly terrain, and find a 11 to 32 selection of rear sprockets allows me to cope with all grades without using the power. 11:32 is in catalogs in 7 speed sprockets, but when I tried to order one none was ever available. If you don't ride up 15% grades you may not need a 32 rear sprocket.
Notice rear sprockets 9 speeds and up have thinner chain, which wears out 2 to 10 times faster than 8 speed chain. I got 5000 miles out of my first 8 speed chain, apparently highly unusual. Some mid drive users with 11 speed chain report 500 mile chain life.