Going the undead route is an excellent idea. You can exp on almost exclusively undead with ease if you go from Shrouded Isle to Kaladim to Freeport. That'll take you up well into the 50s, at which point you'll have a wide variety of spells at your disposal. And, of course, there's Akheva to take you to 65 on undead.
Also, I highly recommend getting a friend to kill the Prelate guy in KaladimB for you. He drops a necro/cleric only cleric offhander that has clickable 4 second cast time Hungry Earth, an undead root that does 60 damage. I got one a while back, and a cleric friend was able to solo with incredible ease in Freeport with it at level 45. Slow, but crazy efficient =)
Also, I highly recommend getting a friend to kill the Prelate guy in KaladimB for you. He drops a necro/cleric only cleric offhander that has clickable 4 second cast time Hungry Earth, an undead root that does 60 damage. I got one a while back, and a cleric friend was able to solo with incredible ease in Freeport with it at level 45. Slow, but crazy efficient =)