Hi ACE67,
As I read it, EACH vehicle counts as a separate unit so coherency rules DO NOT APPLY. The rule for purchasing light mechs is that only similar mechs can be bought this way ( you can't buyt 3 totally different light vehicles for one support choice)
The cool for all "Vehicle Crews" in the game is rated as VETEREN for Bail-out checks etc, which would include Mech crews. ( SOTR Errata page on the SOTR Forum)
Upgrades to COOL only count for core units for the entire platoon but do NOT include any Support choices.
Hope that's of some help.
Regards
PM