Well you generally aren't building AND fighting at the same time. I do one and then the other. Now if you're looking to do both at the same time(like to rebuild and re-equip destroyed ships) your system would clearly be the best.
In my conceptualization of the game, I keep envisioning people speed-building space ships or tanks or whatever and hopping into them to rush to the defense of their teammates. Imagine a DotA like game with masses of weak AI players doing the grunt work and players building contraptions to aid in defense/offense. More powerful vehicles would take longer to build, but inevitably be stronger once complete.
Just to double-check, will Freebuild have some kind of copy-paste, like the old iGob? If I make a cool train car, I'm definitely going to want to be able to resurrect it and 50 copies at a moment's notice.
The current Free build has the iGob, so I would assume they'd keep it, or rework it to be even better. Hell, calc84maniac made a multi-axis iGob rotator that was to be exclusive to Freebuild.
Pretty much this. There will most likely be a conglomeration of iGob-like behavior with vehicle spawning and the LDraw multi-part model format.