I seem to get through brake pads relatively often, but they are really cheap on ebay and I buy up to 8 pairs at a time, replacement is a work of minutes, mostly the front disk.
I have a spare disk that I bought, but up to now not needed.
Please note that both my disks are reversed to what is "current" opinion, as that way they run quieter, and still are flat! Much to the chagrin of the non believers here.....
Chain needs regular oil, I myself use a regular car full synthetic oil, which is relatively cheap in comparison to some of the expensive "Witches Brews" sold for the same purpose.
I had a throttle problem from very heavy rain, that needed a lot of work to repair, but it was not as bad as I first thought. Today I would fix the same problem in hours, not days! But only the once, and I carry plastic bags to cover the throttle if it rains - and I continue riding in ANY rain today!
When delivered, my battery would not charge, and the supplier kindly lent me a "Zer0 Volt Charger", which immediately recovered the battery. Careful attention with regards to charging since then has prevented any further problems.
The headset upper bearing when delivered, had been built with a 2nd lower bearing at the top (1 mm thinner), causing "rough" movement, that eventually the supplier sent me a complete new set which fixed the problems immediately.
Thats about it.
My bike is a Stark, with the 250 Watt motor, and all extras except the GPS tracker, as I already had one!
I do ALL my own work, I save a huge amount of money, as the supplier being in Sweden, means that guarantee work is simply not in for anyone who has two left hands.....
I hope this helps.
Andy
PS. I maintain that a good DIYer, with a reasonable toolbox, that includes a soldering iron and a multi-meter, should be able to fix just everything on an e-bike (or a normal bike!)...or replace a part when needed.