Even RR isn't planning to jump for some time because not enough mods are updated, complete or stable, not to mention the various bugs in version 1.7.2. AE2 doesn't even have autocrafting yet, TE isn't updated yet (it almost is though) and more importantly our primary worldgen mod, COFHCore, isn't updated. Making a world before the latter is updated pretty much guarantees a world reset unless you want to deal with an oregen nightmare.That depends, I wouldn't recommend TE nor a lot of other tech mods if he's going to use 1.7.2, which everyone will use soon.
So really, it's safe to learn TE3, because major packs won't update without it aside from maybe RR, a pack too big for a relative newb to modded MC to jump into.