if your reactivating your old account your old characters should be there, although they might be naked.
ToA had huge amounts of post 50 stuff which was needed it also changed the playing field a lot.
However as things are now things have been made a lot easier and there should be less of the problems that ToA caused.
Main changes, you just need credit and scrolls to get artifact, they train anywhere on anything and easier.
Masterlevels are now easier and quicker.
Catacombs :
Basically introdused lots of stuff to help pre 50, mini quests and inst dungeons, also included some areas that need a good full epic group to get through.
Darkness Rising :
The king returns and offers a nice weapon to his champions.
New epic quest and armour which is fairly decent.
Champion levels (5) which give a minor skill and slight increase in hits.
Demon splatting main quest which is optional but give nice items and allows you to activeate the weapon quicker.
Horses that can carry stuff and move faster then running. (disappear in combat)
darkness rising guide
Hope this helps