Your bike's a fix gear. The most basic bike there is. The drivetrain hardly needs to be clean. The cog needs no attention at all unless the opinion of forum members matters. (My workhorse fix gear gets no attention for 18 months at a time save quick rinses with a light shower setting with the garden hose. I go probably 8-17,000 miles on two chains, then replace the cog, ring and chain.)
Chain tension (actually lack of tension) is important. I see to it the chain never goes tight over several full pedal revolutions until I know the chain has gone completely around. Super tight chains seem to be the popular thing now, but if you go the velodrome and watch the big boys race, you will see zero tight chains. That's right. None.
I googled KMC and found this:
https://kmcchain.us/chain/k710/ I think you have a K-710. A BMX chain. It will work just fine but it is compete overkill for road riding. You hardly need peened rivets/pins. Regular rivets work just fine on 1/8" chains for our use and can be driven in and out repeatably with no damage to the side plates. (A chain I really like is the standard Isuzue chain, roughly $25. Very reliable.)
Bars and stems are so personal I won't go there. Plus I am such a drop HB guy, I know about nothing re: any other shape.
Ben