Maintence levels on the TTR will be the same or higher than a WR/YZ F. Main reasons are the smaller oil capacity, air cooling, frame design, poorer suspension etc.
Remember you still have to change the oil, adjust the valves, clean the aircleaner, lube the chain, lube the bearings and linkages, replace disc pads, replace seals etc etc etc Thats coming up in the future.....
Dont worry though the TTR is fantastic trail bike that will last for ages. The WR/YZ F are race bikes and need to be ridden as such. The TTR is a easier to live with bike great for just about anyone and has that little magic button...:)
The TTR's and the PW's must be the biggest smilly :) bikes in the Yamaha Bike range.
For the seat get a new cover or water will destroy the foam. If you get a shock on orig price try Ballards for aftermarket one. I think the uncorked Staintune will need you to go up one main jet size at least.