4) How on earth do you order your corpsman to heal your other injured unit ?
If you are the squad leader use space bar select your corpsman and click on the injuried unit, or serlect your corpsman, hit 6 and select the heal command.
5) How on earth do you re-supply with ammo your unit/s ?
You can tell them to take ammo with the 6 key (not numpad) they will take dropped weapons.
I think you can also choose the loadout of soldiers when buying weapons.
I don't know why you have so many issues, I've the full game but I've played the free version to show the game to a friend and we could join servers and play as with the full game.
Try another server or try to play some coop missions and tell us if yo experience the same problems.
Be careful when posting on this forum, it's an arma forums so there is a lot of fanboys choose your words wisely.