i posted the link to a manual in the other thread, it might still work. that should send you in the right direction with it.
i dont think a $60 tune up on an atv is worth it, outrageous actually. NGK has my heart, just standard plugs.
its pretty common to have a little metal on the drain plug as well, nothing to be concerned with unless theres a bunch on it all the time.
cant help with the valve covers, check out where your exhaust comes out and intake comes in, those will be the valves on each side.
steve
2019 Maverick X3 XDS Turbo R
2003 TRX 400EX
2016 HONDA RANCHER