Oh how cool! I played TFC quite a while ago when it was pretty new. I liked the idea, but there just wasn't enough content. But to combine with steampunk? Neat!
So I've been playing with it and I have a few observations:
1. With a LOT of effort and copying from other FTB servers, I got the server to run. It doesn't download the necessary libraries to run. Also, the first 9-chunk radius around the starting area was all default minecraft terrain. Fortunately a snowy mountain spawned near the edge so I could climb up to the TFC height. But it also meant that I had default dirt, cobble, and other stuff to play with...
2. I see the others are already suggesting rewards of vegetables and such (and their seeds) for early quest rewards. I was also going to suggest that. I didn't think of having mobs drop them (or seeds), but for weak mobs you find early that might be a good idea. Especially those willy blue kobolds that keep spawning all over the place.
3. I also have been finding only lore books in chests. But these are not "dungeons" but rather the "points of interest" from Twilight Forest. For example, the overland maze. The chests in these have nothing but lore books in them.
4. Twilight forest is probably responsible for the spawners found underground. I know that that mod uses them to create large concentrations of monsters in certain areas.
5. I personally don't think it should take so long to chop a single block of wood. It takes a whole minute to chop down a whole tree or a single block of wood. Is there a way to make the time dependent upon how much you are actually chopping?
6. Quest rewards of a "single" piece of coal or charcoal is pretty much worthless. It should be at least a quarter stack or something entirely different that has value in singles.
I'll post more as I come across them. I don't have a lot of time to play, so it might take me a while to get to the more advanced stuff!
P.S. I highly recommend you have the quest for the power source BEFORE the blocks that need the power. Or, alongside it as a multi-part quest. Or something like that...