In skimming all this I just kept thinking of what I tell my players.
You can try, but you can only do so much. If you don't have the right medikit/first aid kit (two diff things) you are at -6 right there. Why, because you don't have the tools. You can be the worlds greatest surgeon of all time, but you aren't removing an appendix with just a pocket knife and the sewing kit you got issued in basic... well not easily anyway (yes I've seen an appendectomy).
Of course there is a difference between 'first aid' and something more significant. Growing up I had these two great Korean/Vietnam era army first aid kits. Went on the web belt tied to the leg tons of bandages etc. I took them on all our Boys Scout campouts etc. I actually got to use one one, a friend stepped on glass I pulled out the big bandage-large pad of gauze to go on top of the wound and then the two ties to go round-and-round the foot and be knotted over the bandage. The doc at the ER was impressed by the job I did, even more when he found out I was 13 at the time.
If I didn't have that first aid kit I could have torn a shirt wadded a piece up and the rest to tie it down but not as good.
A medikit comes with more, as the book says starts with like BP cuff etc and goes up from there. First aid is "treat what you can see/determine at the moment. Medics and Paramedics deal with more. I can clean your wound splint your leg bandage that cut on you head (a little antibiotic cream too)... These folks can get your leg splinted in a nice rigid air cast, on a real back board, pack your wound after cleaning, give you pain meds, check your vitals listen to breathing (and know what they are looking for) etc. That requires more than is in ANY first aid kit.
So, no gear/kit I do -6. As the kit is more complete for what is needed I drop that down. Best they get is +0 for having the right medikit for the job.