In the .aiw file you can see under
"[GRID]" how many grid positions there are. Usually there are a lot of them, so that is not a problem
"[PITS]" how many teams there can be on the track. Usually there are 3 garage positions and one pit stop position for each "team".
If cars have the same specified pitgroups in the .car files, they will be considered a team on track.
If the cars don't have pitgroups, the teams locations and garages will be filled randomly, and if there are not enough team positions in the track, the garage spots will be filled with "mixed" teams.
Increasing cars in the .gdb files will probably cause some problems in the pits, but it is not dangerous to try
Often the teams have two good garage spots and the third located between them, making it look very crowded. Sometimes the third car is parked inside one of the other cars. It works, but it looks silly