First off, try my medic loadout and see how you like it:
POUCHES: 2 medkit pouches filled with basic shit
WEAPON: The good ol' shotty, good at making the runners scared shitless... at least most of em
BELT: Lifesaver belt, filled with basic shit + epinephrine bottle and ImiAlky
SATCHEL: Red Cross for da win, filled with 2 defibrillators, advanced medkit, hypospray filled with epinephrine, a suicide/offensive nade and buckshot.
ARMOR: Medium filled with 3 buckshot
BLACK/BROWN webbing: MEDEVAC stretcher, roller bed and 3 buckshot
HELMET: filled with 2 protein bars
Now, to answer your questions:
1. Wanna scare off runners and lurkers? Take the shotgun, they will most of the time(if you don't encounter BOO in a 1v1, then you're kinda dead) run away in fear, load it with buckshot and you can easily 1 shot them if you get them at point blank, 10/10 weapon for medic.
2. Yes, give them 2 pills of bica and one of quickclot, wait a bit, then give them the 3rd pill of bicardine to minimize the time of overdose. Better than evacuating them, which most ungas will refuse.
3. Iron is useless, my opinion.
4. Please don't throw nades if you're behind marines, it will bounce off their backs and end the assault or blast the whole cade line up. If you're sure you won't get moved by marines and you're on the front, in the cade area I mean, then yeah, throw it and make the xenos mad.
5. I guess so, I never used the revolver... only once as survivor and I was learning how to actually use it.
6. No, keep the autoinjectors, you can't open pill bottles and they're gonna keep the unga alive until you heal them.
7. Squad engie... just read the wiki and a guide, I am sure there is one. Go on Bravo squad and build the FOB at first, then go MT and learn how to repair reactors and shit. Also, learn how to repair APCs and hack shit, very useful... Cargonia? Pfft, hope there is a RO or CTs that can help you, if there is none, tell command you're kinda bald and they will 100% help you. Don't be afraid! We all started somewhere and we got better and better. You will too!