1. since the eidolon cant be targeted separately and effectively has no hp(the hp is simply temporary hp that i get), would the fused form still be immune to cold for instace?
2. the eidolon has no saves of its own, therefore i have to use my saves?
3...
4. leaning towards skilled tank right now
to it being fairly generous, dont forget that i lose some caster levels due to the template, especially the racial hit dice hurt a LOT!