Welcome to Librarium Online!
i just wonna be sure..
is it allowed to play with AoS in tournaments as any other army?
and can someone please tell me a bit about this army, as i've thought of playing them...
are they fun and a tough army?
and is it true that i (if i have 3 grave markes)can cast From Death Awakened 3 times in ADDITION to all the normal spells from the necromancy list??
Yes you can cast as well, but you don't get necromancers so your casting is limited.
Yes, they are completely tournie legal.
For information on them, have a look at the stickied Sylvania tactica in this forum. They're a great army, I love em.