The first aid skill is not as useful since there is no enemy NPC or wild life threat to cause injury to player at the moment since zombies are the only enemy threat.
Currently the way I level up my first aid skill is to injury myself to increase the skill by climbing through a window with broken glass in the frames just make sure to have some bandages a suture needle or needle and thread in case you get a wound injury.
Do you know if there's any truth to whether having a higher level of it reduces the chance of zombie infection? ...Like, if I had level 10 first aid, would my chance of being zombified from a zombie scratch be reduced to 15% rather than 25%?
As far as I know, healing times, infection, and also how much information you get about each injury (severity, healing).
I couldn't tell you the exact differences between the levels, but it's good to have somebody with the skill in MP. It's pretty difficult to gain XP otherwise.
I don't think there is a real to change the base map, since they are mostly clean for a reason.
There are already event houses that rely on RNG and are supposed to represent some kind of situation happening, like an overrun home base, a suicide, or homes that have already been fully looted with one window smashed in. I wouldn't mind expanding on that, maybe increase the odds for starting later into the apocalypse with the erosion mechanic.
There is actually more than you would think, what with shelves being populated by books and even themed loot lists based on the profession. Apart from that, the chances of encountering special homes that have the remnants of the former residents (suicides, dead bodies, obvious loot) there is also cooked food still on the stove.
This is something likely to improve naturally with the inclusion of NPCs.