Most of the time, as far as bad guys go, I'd say up the number, to give the good guys a challenge to beat. Unfortunately, this is not the case with Transformers. The more Decepticons there are, the more bad guys are there to simply get blown away by the military, or the occasional Autobot. Usually, having a ton of bad guys would really raise the stakes, but in Transformers it does just the opposite. Having all these Decepticons around just makes them seem like wimpy bad guys, as they all get taken down instantly. Personally, though, I love the movieverse design aesthetics. For me, having more robots in each film is fine, because then we get to see more cool movieverse designs.
I would say YES, enough bots and cons...tho we don't have confirmation on all the robots and names yet...but I would prefer they keep it to a dozen or so total..give us a chance to see the main character bots in action--both verbal and physical.
Depends on how they are used. They are really going to have to increase the bot time though if the robots are going to be more than just silent background scenery. Or the Transformers equivalent of the cantina scene from Star Wars. It also seems like the number of Decepticons is really really low unless they have found way to make the Decepticons way stronger and dialed back the strength of the Autobots and the military. Not only do you have Prime and Bumblebee killing the Decepticons left and right but you've got their buddies in NEST to throw even more fire power at the bad guys. The way this list is so far it's looking like the Decepticons could be outgunned and outnumbered.
Actually they should have actually seven robots on each side with actual character. They can have more if they are nameless cannon fodder. Worked well for Lord of the Rings.