As stated multiple times before in this thread, the transformer emerging from the cloud of smoke is Lockdown. Galvatron is the sliver one slicing the car in half from the superbowl teaser. Whether or not Galvatron is a reincarnated Megatron in this adaptation is yet to be seen.
I'm not sure in what continuity the matrix of leadership has ever derived from the Star Saber. In most incarnations it either comes from Vector Sigma (the most advance AI on Cybertron built by some of the original 13 primes) or it is gifted directly from Primus at the the core of Cybertron itself.
Grimlock was always a big guy, but by no means the biggest of the individual (non-combining) transformers. Certainly to be the biggest thus far in the movie verse though, and rightfully so. Grimlock is intimidating in every way (but intellectually) and should be kept this way for the movies.
I imagine (and hope) the downgrade in the visual complexity of the transformers appearance is a result of two things. The first being the relative rushed schedule/timeframe that Bay makes his movies within. He is well known as a rush rush rush type of guy, it doesn't surprise me that reducing the vfx processing time/work load would help hasten the movie to that release window. The second and larger pipe dream for this is that it would allow for the transformers themselves to have more screen time vs their human counterparts within a similar budget given this movie is shorter than the previous three. If I remember correctly, in a 2+ hour movie, the original Transformers Bayverse movie only featured the Transformers themselves for about 11 minutes of screen time. It has increased with each installment since then.
The biggest issue I have with this movie though, is the announcement of The Rise of the Dark Spark. Somehow this movie is supposed to tie into the aligned universe reboot. War for Cybertron, Fall of Cybertron, the Prime series show, and the Covenant of Primus book have all been inconsistent in providing a concrete agreed upon sequence of events. Trying to establish this movie verse in that continuity when Bay has done so much damage to the origin and characters already is puzzling. I always thought the movie verse was its own continuity, and believe it should be kept that way.