I know they're working on big changes that will change the UI, so for right now I'm going to answer a few things for you (what I know):
2. When I have added a friend all I can do is invite them to a game and not join theirs which I more then once want to have.
you can join theirs - you just need to exit the lobby you're in first. if you're in a lobby, it'll default to inviting them. if you're not in one, it'll default to joining others.
3. When I'm joining a game that has already started I might end up playing as a gunner on a gun I do not know (as a new player to Guns of Icarus) having a way to see details of the ship you work on just like you can in the lobby would help through a lot of these situations.
I found the Practice matches to be really useful for this. If you want to practice with a real human being and see me on, shoot me a message in game; I'll start one up and invite you if I'm not in the middle of a match.
5. Looking at the achievements it often say 'Until next level: 1(or 2,3,etc) I do not really know what it is but I figured it was the amount of achievements left until level up, but if that is so it is not entirely correct since I have gotten like 3-5 achievements on a single run and not gotten level up. or is it some special achievement? if so then you need to explain it better.
It is achievements to level up, from the Log tab, not to be confused with achievements from under the Challenges tab.
And I'm going to point out you can hit Q at any time to see the achievements you need to level for the class you're currently running as.
Muse, take note of these when you make your changes!