You have 5 Wave Serpents, 4 of which have a range of 24" and one with a range of 48". The 4 S cannoners have a decent chance at damaging rhinos, but you are goign to have to start getting rather close to get the shots off, this means your manueving cover to your advantage and lining up unexpected shots will be heavily hampered. I suggest scatter lasers as a minimum for serpents to get that extra shot and 12" range.
EMLs are fantastic for popping armor as you have your fire dragons for the 13+ armor stuff.
Seer council on foot is limited in a lot of ways. You can't assault out of the vehicle if it moves so you have to line up your assault, making it predictable. Once on foot you are moving sllloooowww and if you want to reembark you eat up another round of movement moving to the serpent and getting in. Smart opponents will try to pop this serpent asap and force this unit to slog across the board effectively hindering 300pts of your list.
DA Bladestorm are great don't get me wrong, but against marines they are lackluster without Guide/Doom. WARNING MATHHAMMER: 27 shots 66% to hit, 50% to wound = 9 wounds, 3+ armor = 3 unsaved wounds. 5 shots 83% to hit, 50% to wound = 2 wounds, 3+ armor = 0-1 unsaved wound. So for 152pts you got off 4-5 unsaved wounds, you can't fire next turn, and you are sitting in the open under 18 inches from the survivors and whatever else may be there. With guide and doom you push that math up significantly.
Fire Prisms, these are your biggest anti-marine in the list.
Str 6 AP3
TL large blast with a 60" range will decimate whole marine units at a time (and it really NEVER gets old). These things will get a LOT of love from long range
AT from anyone that has ever seen them. Without holofields they have little to no protection from becoming a smoldering wreck. With holofields the cost goes up quite a bit, but at the same time you reduce the chances of a wreck/explode result to ridiculous low chances. it increase the chance of shaken/Stun/Weapon Destroyed, but remember a weaponless prism can still ram and contest.
K now all this said, your list isn't bad it'll jsut have some rough matchups. If you already have all the pieces for this list then take it for several test spins and get a feel for what needs tweaked. I can tell you till I'm blue in the face what to do, but unless you experience it means nothing
If you don't already have all these pieces I would suggest..
Eldrad
Farseer
4 Serpents
2 packs of Fire Dragons
2 Packs of Dire Avengers
3 Fire Prisms
and make sure you magnetize stuff to swap things around as you learn.