So many of these missions i've noticed are pretty hard alone, some may find it easy, but here's a tip for missioning. Now there is a reason behind why they want you to be in a squad, its because they want you to work together, make a team(at least i think its why). Anyways on with the missions!
Free All Bases- Now for this i recommend a part of maybe 2-3+! Now i mean if you can handle each boss/mini boss by yourself, go ahead! But this is pretty damn difficult alone...you have to capture 5 bases from aliens. You got a boss/mini boss and probably two little ufo's. Recommended Guns: Any Purchaseable Gun. Just a tip for beating the big ship, shoot it from above or the sides. It can't really move anywhere.
Destroy Three Powered Towers(i think thats the name)- Now this one, this is the hardest one and i recommend 4-5+ players for this. It also gives the highest of experience! Basically you destroy 3 towers with 2 bosses floating around the area while near the towers you have to destroy are unlimity spawned ufo's. Already sound difficult? Thats because it is...Recommended Guns: Any Purchaseable Guns.
Rescue 10 Rebels- Now this one is probably the easiest one out of the already 3. All you gotta do is use your knife to cut loose the rebels, BUT you have to fight this alien pyrates i like to say to get to the rebels. Now you can do this with any amount of party members, easy! You don't HAVE to fight the alien pyrates, but if you want experience, you will have to, then again you can also gain experience t cutting the rebels loose. Recommended Guns: Any purchasable guns and the beginner gun.
Anyways i hope this helps in some sort of way to you guys, and yes i know, i've already made a guide before. I just found doing a guide like this to help you guys a bit, and hopefully it does!
Enjoy~