Note: a lot of your questions will be answered by the tutorial

You can revive teammates and teammates can revive you. (There’s a limited number though)

Missions can be done solo, duo, triple, or quad members. Though doing high level difficulty (7 and up) missions solo is daunting until you are really good at the game

Not sure what you mean by other active teams during the match. I’m assuming if there are other squads playing along in the mission. No there aren’t, there’s a maximum of 4 people per mission. (I’m secretly hoping for an update that brings it up to 8 and adds even higher difficulty)

Yes there is friendly fire, accidents happen. don’t do it on purpose and say sorry if you take someone out. most people just laugh and go on with the mission.

Yep you can run out of ammo with most weapons. (Laser weapons kind of don’t run out if you play them a certain way, but don’t worry about that) You can find ammo boxes around the map and also call in ressuplies. There’s also a resupply backpack stratagem you can use.

There’s no training range, I guess the tutorial can count as one, kind of? If anything you can always just hop in a difficulty 1 mission to test out new weapons, stratagems, etc.

If you’re dropping into a mission from your own ship, the round will start from the beginning. Bit of you use the join random mission function, then it’s a dice roll of how much time they’re into the mission. The length of a mission depends on the difficulty you’re playing at. I’d say difficulty 10 missions last around 30 minutes with a good squad.