I'd like to go for a 4 unit as my first multi so keeping my eyes peeled and offers ready...tbc

So a stain like gel stain will mask the grain, as it sits on top and doesn't penetrate.  

Since, generally speaking, lead paint only poses an immediate hazard if it's on the surface, or if there's peeling and chipping paint and subsurface layers are exposed, if you want to go the cheap and easy route you can get a $10 lead paint test kit at Home Depot and check various surfaces (just keep in mind the contractual contingency may only apply if the testing was done by a professional, according to the standard verbiage in the NH P&S). 

You can get peel and stick wallpaper that might work, but unless it is neutral I wouldn't do it and even then do it with the understanding that it may not hold up well. 

He will take photos of anything that is a concern, such as peeling or old roof.

That is literally paper thin finish peeling off... 

I know when i was going that route there could be no chipping or peeling paint, must have handrails on both side of stairs/steps greater than 3.....etc.

and painting walls definitely seems like a DIYI just have one more issue there is some painting a very small section on ceiling that seems to be getting peeled off please find a pic is this something also a DIY to fix?

He smokes a lot, sometimes inside his unit but he masks scent with incense that makes my entire property smell like a casino. 

This house has been like peeling back layers of an onion though.