To change reinforcement number, you must edit files having the *.LUA extension. For example, open "bes1a.lua (Located in "BFBuilder\Assets\Mission LUA Samples\BES\") with Note-pad, and then, scroll-down in this file until you find two entries named " SetReinforcementCount". You'll see a value next to these arguments : This is the reinforcement number for each faction. (Attackers and defenders...)
Can you make vehicles bigger? Like the ones that are already there?
To re-size existing vehicles, you need to convert them in a common format and open them in a modelling software...