Visually I envisioned the squad selection to look something like this (logically you wouldn't know where the enemy would exactly be coming from):
Where basically every arrow on the overhead map represents a squad that is fighting (the mapper would basically define the max amount of squads / minimal % player size per squad). Where in this situation a player could join a squad by clicking on an arrowhead that belongs to the advancement of a squad. So you instantly know what squad you're joining and where in the world that squad is fighting.
And my idea was that the squad leader could basically select out of a few possible paths/spawns made available by the mapper which path/spawn his squad will take.
Using the overhead map like this gives newer players an idea of how many different squads are fighting currently for his team and at what location. Together with instantly seeing where his own squad is being deployed. You could probably compare it to a quick mission briefing.