[noob question] what is squad spawn? do I need to play all classes to earn stuff

So, here is the situation: what you saw was squad score (not spawn), which is part of the score that you get from participation in the actions with the squad you are in; these include:

• Following orders of squad leader (attack or defense); Objective that the order was placed on will have green marks as a part of its icon.
• Squad healing, squad reviving, squad resupplying, squad spotting, squad repairing
• Squad assist counts as kill
• Squad suppression assist
• Squad spawn on you

It already is included in the score that shows on the scoreboard, but level progression bar shows it separately so that you could see exactly how many points you got from these actions.

About weapons, You will miss out a little bit. A couple of pistols can only be used once you get rank 10 with a certain class. I'm not sure if each class has its own at some point. What I'm sure of is that Scout unlocks the Kolibri (troll pistol doing 5 damage on point blank body hits and 25 on headshot) and Medic unlocks the C96 (10-round semi-auto pistol).