It’s a surprisingly small number! As you say, there were the Dinobots being built by Wheeljack and Ratchet, through extended montages that showed various stages of their assembly:

But we don’t actually see the Constructicons being built by Megatron, he only says “They were worth the time we spent building them.” Season 2 would retcon that and depict them as coming from Cybertron, where season 3 would imply they had originally built Megatron with this lone visual:

The bodies of the Stunticons were created by Megatron through another montage sequence, as he rebuilt them from Earth cars:

while their opposite numbers, the Aerialbots, were rebuilt from Cybertronian spacecraft into Earth jets by the Autobots in the time-gap between Part 1 and Part 2 of the two-episode story that introduce the two teams.

Then there was Trypticon, who we saw the Constructicons build out of a human city, and later, Grimlock built the Technobots (with the actual constructicon taking place off-screen, the show cutting away right after he got these parts together and started fiddling with them, then cutting back):

And in the series finale, Lord Zarak rebuilt the Nebulan Hive’s underground city into Scorponok, while Spike did the same to their abandoned surface city, turning it into Fortress Maximus, but in both cases, we only saw the opening stages of rebuilding, with the rest happening off-screen, the reveals of the city-bots being saved as surprises.

Yes.

Just trust on this one.

The answer is yes.

Unless there’s some specific instance you’re referring to involving some special circumstances - yeah, G1 Grimlock and the Dinobots are much, much larger than BW Megatron. Maximals and Predacons are all smaller than G1 Transformers because of a race-wide upgrade that involved Cybertronians downsizing their bodies to conserve energy. The G1 Dinobots, by contrast, are all about head-and-shoulders taller than Optimus Prime.

Now, of course, in the Beast Era, Grimlock is known to have been one of those Autobots who downsized into a Maximal body, in which form he’s about the same size as BW Megatron.