Saurus Astrolith Bearers carry the most weight in a Seraphon army outside of the Slann in my opinion. I am always looking to fit them into my list. You could also take a Skink Starpriest and switch back to Great Remember for your Slann's trait allowing room for some addition Boltspitter Skinks as well. I am not sure which option is best at 1k. If you want to remove enemy models quickly then the Astrolith Bearer route is probably preferred. Skinks being able to reroll their failed hits from Proud Defiance become surprisingly killy. You could also plan to go a hybrid of these two paths by taking the Astrolith Bearer and summoning a Skink Starpriest. Great Remember at 1k is exceptionally powerful. I would plan to get a Starpriest on the field and drop the Vast Intellect trait. Ideally Summon Starlight is cast from a Skink Starpriest and won't cost your summoning. You want to be using all your Slann's spells to generation Celestial Conjuration points.