Hi! I would like to ask for advice:

1. I accidentally scratched my door against a nail unseen against a dark and narrow passage. It's a a four-inch single white gash, which is pretty deep. Altho it's obvious it'll need a real paint job to fix it, what can I use to at least camouflage it for now? I think there's a tube-stick kind of application, but can that work for a deep gash? Or would that mess up the look of entire door that it's better off as is? Someone told me not to use rubbing compund either if it's just for a portion (not the whole door) and if i dont know how to expertly apply it.

2. Someone smeared paint on small part of my bumper (white paint vs dark car! i'm hesitant to scrape it off since it'll damage the car's paint-- is there any solvent i can use that can remove the paint without harming the car's surface?

3. lastly, everytime i start my engine, it's a hard start (3-5 ignition tries, then have to step on gas for a while) i had it checked twice, first i was told it was a battery problem. however, after i got a new one (and new spark plugs), the problem's still there. then i was told it was a valve toppet (?) problem, which i then had fixed during a tune-up, but the problem persists. in the end, i was just told it wasnt fixable, it's part of the car's normal working to have a hard start-- is the latter true or they just dont know how to fix the problem?

apologies for the kilometric questions, i didnt want to open individual threads for them to avoid cluttering the forum.

thank you very much in advance for whatever advice you can share!