Mixing dedicated transports/FA transports

The rules for dedicated transports restrict any other unit from embarking on that transport at the start of the game, but it doesn't say that the models NEED to start in the transport. There's no restriction that I can find that says you CAN'T purchase a DT if your squad exceeds the capacity.

So I wonder if the following examples would be legal so long as these units are in cohesion to their transports:

10 Wracks, 1 Dedicated Venom, 1 FA Venom
15 Wyches, 1 Dedicated Venom, 2FA Venom or 1 Dedicated Raider, 1 FA Venom
20 Warriors, 1 Dedicated raider, 1 FA Raider or 1 Dedicated Venom, 3 FA Venom

This wouldn't be like SM Combat Squad in which they become separate units, they would just have to maintain proper cohesion. If this is even possible would this mean the vehicles become a squadron when it comes to allocating shots/penetrating hits despite all being purchased separately?

Page 80 BRB - Transport capacity, first paragraph is the relevant rule.

Short answer is 'no, you can't do this'.