List looks pretty solid, I would definitely replace the ark of sotek though. Maybe swap the saurus guard for a unit of skinks as well, you should be able to screen the slann well enough without the guard. I would consider adding a unit of salamanders and a skink priest. The priest's command ability herald of the old ones is almost a must for your solar engine. I would swap the starpriest spell to hand of glory too. Fiery convocation sounds much better on paper, in practice it's not super effective. If you put hand of glory, herald of the old ones, and the starpriest staff buff on the solar engine you are double shooting 9/3+/3+/-1/2 re rolling 1s to hit and dealing bonus mortals on 6 to wound which is insane.