Top end rebuild??

I am new with the dirt bike scene and looking into checking out my engine on the 2003 CRF450R. I bought it used and it wasn't ridden much. I do not know how many hours are on it except what I have driven now.
I have read that the intake valves are better if they are steel and a good piston is the Wiseco. Should I just go ahead and replace the valves and piston if I am going to start looking into checking the engine over? The bike starts fine cold and never a problem restarting once hot.

I read people buy the top end gasket kit and they say not all gaskets are there. What should I be buying and from where. I found the piston kit by Wiseco online and Faction steel intake valves with heavier springs.
I have read to just replace the rings after 20 hours. What am I missing here?
Recomendations?

I looked at Service Honda but thought rockymountainmc was a better site. Where else makes buying parts simple online.

At rockymountainmc, I found valves by Kibblewhite Black Diamond. Should I replace the valves and would I need to have someone shave the valve seat? The way I am understanding this, the after market steel valves seldom need work done after install. Sounds like the piston alone will improve the bike also.
I read about kits not having the bearing when doing the piston? The kit from Wiseco has the piston, rings, and wrist pin. Do I need more yet?

Just looking for suggestions before I set a day aside to do the repairs and inspections. Would prefer to have all parts available before I do and not need to repeat the tear down. Any help would be great.