I also agree that that passage means no Spellcraft rather than no Know (arcana). I also like any three Knowledges.
Alertnness might be just about the only sensible feat for these.
I think these shouldn't really have a tactics section (I can't remember if symbionts usually do). As for flavor and description, any ideas?
Well they don't have any attacks, so a tactics section would be a trifle superfluous.
What would you put in it? There is little strategic effectiveness in "refuses to offer advice but is willing to discuss philosophy".
Here's a sample from another symbiont with no attacks:
Fiendish familiars do not engage in combat, nor do they specifically aid their hosts in combat--although the enhancements they offer to spellcasting hosts can be significant in such situations.
Agreed.Just copying that over would do the job.
Agreed.