I wouldn't recommend adding TE, Forestry and Railcraft if you want to learn each mod at a time just because they're not actually direct additions to Buildcraft, as they add a lot of new, independent content each, and if the idea was to make learning less overwhelming that won't accomplish the objective at all. Actual add-ons to Buildcraft you might want to put in that won't be so overwhelming and that actually add to the mod are mods such as AdditionalPipes and Logistics Pipes, which improve upon existing BC fundamentals instead of adding new concepts like new machines or Forestry's beekeeping, which is one of the most complicated and detailed features to learn among all mods currently in FTB.
Answering the OP, as far as technical issues go, FTB won't be troublesome at all, but the learning curve might be quite steep for a Minecraft newbie, considering it already is pretty overwhelming even for long time minecrafters. It is extremely fun, though, so if you're up to it, go ahead. There are many different places you can learn from. While there's no FTB wiki, the mods' wikis are an obvious resource (Google for them, too many). Also, you might find the Technical Pack wiki a nice place to research, considering the packs have a lot of mods in common. You might also be successful trying to learn keeping track of a Let's Play, and for that many people would recommend Direwolf20. Waiting for his new single player series may be a good idea, though, seeing as he's not nearly as descriptive and educational in his SMP series, where he spends most of his time visiting the other players.
By the way, as a last recommendation, disable GregTech (you can do it from the launcher). As to why, many people have explained it before, and I'll be brief: it's a mod basically designed for some ludicrous end-game content but mostly makes things harder and more complicated. Also, because it's such a new mod in the scene and because it changed a lot of the default IndustrialCraft recipes and mechanics, it'll be tougher to learn things, because documentation might not match the actual game. Once you get used to IC2, take a look at its documentation and see if you like it or not, but for now you shouldn't use it, as a new player.
Good luck and have fun with your mods!