For my Slann I was thinking of putting the following disciplines and I was hoping for a second oppinion on the ones I chose. Focus of Mystery The Focused Rumination Higher State of Consciousness Unfathomable Presence The Slann is not in a unit of TG - he is on his own.
Focus of Mystery-Great Choice, but can be dropped if you need the points. The Focused Rumination-Don't leave home without this one. This makes the slann the ultimate spell caster. Higher State of Consciousness-Etheral-you have to have this if you want to survive with a solo slann. Unfathomable Presence-Magic resistance is good, but this is another one that can be dropped if you need the points.
Unfathomable Presence: One of the good points of magical resistance is that it gets passed onto to the unit the Slann is in, however since you say you are running the slann solo it is basically a 1+ Ward against magic (which is ultimately a 2+ ward) Another approach to consider is the Divine Plaque of Protection instead if you have space in your magic item allowance. It is only 3/5 th of the price of Unfathomable Presence and gives you a 2+ ward against ranged attacks. Most (maybe all?) spells that will harm you are ranged attacks thus this gives you the same protection as Unfathomable presence. As an added bonus it is also a 2+ ward against magical shooting such as runic dwarf cannons and Skaven weapons. So this is a cheaper alternative to consider if you have space in your allowance
When i run a slann i like doing higher state of consciousness with divine plaque of protection so if magic missle get shot at me i have a 2+ward save and then 3 jungle swarms around it so the only way you can kill it is gettig Past 1 would from swarms and beating it in combat resolution or you failig. 5 2+ saves from a magic missle