This is about all the information you'll get for most purposes.
Otherwise if you ask around in game as a necro, you'll definitely get some hints/tips about what you might need to do.
Aside from that all I'll say is: Lich - hardest, prays required in a certain fashion. Mummy - Still difficult. No praying required, just a quest. Wight - easiest.
You could know ahead of time what you're aiming to do, or figure it out later. Depending on your level of masochism you could pick accordingly, but shouldn't expect success
