First maintenance

[PG tips]

I don't have the bike too long, not put much miles on it.
I've just done a few things to the bike, to give it the once over before I start putting up some miles
I changed the oil and filter, but a few other q's, if people can offer opinions?
When I checked the air filter it looks clean, I've no compressor so can't blow it out from the outside, could I vacuum it from the inside?
I checked the plug and it looks good/gap ok, was expecting it to be stuck in, but surprised how easy it came out, it was almost loose!
I think someone may have put on some anti seize grease at some point and the grease has dematerialised in the meantime, pleasant suprise, handy having the toolkit too as my car plug socket is different length/diameter.

I checked the sprockets, they seem ok, but even though I lubed the chain (from a can) , the rust is still peering through, I will check the manual document again, think it said something about not putting grease on it due to o-rings?, do people paint a small amount of grease on? dont want it flung everywhere.
when I checked the air filter box, there was a bit of a smell of petrol in it, I presume its just coming back from the carb and what looked like oil (a small amount?), when I opened the drain for the air filter box, a bit more oil leaked out (not too much), is the drain to catch oil blown over from the breather hose, just wondering why they do it via the air filter box? surely that might contaminate the filter?

I think I will try check the valve clearances, but read that a special tool is needed??
but I will run it to check oil level/take it out for a spin before doing any more work anyway.

Mostly want to ask, there is some slight corrosion on the forks, I think it might have been from stone chips as its only on the front
it seems to be mostly above the level where the forks dip to when braking, any ideas whats the best way to remove it?
Someone I know recommended metal polish but all that does is clean the chromes part, I thought it was like a rubbing paste, I'm beginning to think I might have to sand them out lightly but would like to get some advice on that, dont want to create a starting point for rust.