Note that not everyone will have exactly the same interpretation here. My personal ruling is that backlash counts as your catch for any toughness or recovery powers. I've seen other people rule that you get the full effect (including toughness armor) against backlash. So, talk it over with your group / GM.
Having it count as a Catch is interesting; this would mean that the extra stress boxes from Toughness would be unavailable for that purpose, nor could Recovery powers be used to clear consequences faster. I actually prefer this take on the matter (as a house rule), since it prevents what I see as abuse of physical recovery powers to enhance spellcasting.
The armor question seems to have a
very clear answer in the RAW I quoted previously (YS250 sidebar), though. If you decide to houserule that away, what optimal spellcasting build wouldn't include the following stunt (compare to Tough Stuff, YS152):
Resilient Psyche: Your mind is able to shrug off the mental trauma inflicted by using or being abused by spells and supernatural attacks. Against such sources of mental stress, you have a natural Armor:1 (which stacks with other forms of protection). This does not apply to any mundane/non-supernatural source of mental stress.
Unlimited
free spellcasting up to your Conviction plus power specialization (and reduced stress for more powerful stuff),
and persistant resistance to mental attacks such as Incite Emotion! What's not to love? Spellcasters with "Inhuman Mental Toughness" would be downright ridiculously overpowered, in my opinion.