Engine rebuilding Q's - Cylinder plating and new valves?

Getting ready to rebuild my 06 TE450 and want to educate myself a bit more on the process and needs. My bike has probably close to 4K miles and over 150 hrs on it. Plan on main bearings, rod, piston/rings, timing chain, and assume new valves. I havent had the engine dissambled yet. I am considering doing much of it myself if I can (have torn other two stroke motors down, but not a 4 stroke yet).

1.) I assume that the cylinder must be recoated. Heard Millenium in WI is the best. How do you know if or when it needs to be replated? Is is just like a two stroke where the diameter of the cylinder has grown from friction beyond the factory spec? Or is there more to it?

2.) How do you know when the valves have outlasted their useful life? Beyond the obvious of they are no longer seating/sealing.

3.) Are there aftermarket valves available? Is there any advantage other than availability to using them?

I am not looking to have a performance engine built, just a reliable and long lasting one. The 450 has more than enough hit for my use.

hi SFTE,
I've got an 04 TE450 that got a top end freshen up at about the same milage a year ago.
I replaced the valves with stainless steel ones from Hall's (and the springs they recommend to use with them). The four valves and springs cost about the same as one genuine valve from the local (at that time) dealer! They wanted $387 per valve!
I was advised to check the valve seating before assuming it would need the seats cut and found they all had a good seat. They just had to be reshimmed.
The barrel was like new with no appreciable wear. I changed the rings however.
The parts book listed two different pistons with different ring sets and the only way to determine which piston I had and therefore which rings I needed was to disassemble it and check the brand cast into the underside. (mine had an "ART" brand which is a big Japanese OEM) Hope this helps