Not generally in themselves, but for some purposes, those levels will count as levels in the class they advance

D&D 3.5e

Does anybody know of a list of Templates by Level Adjustment? Specifically +2/+3 LA ones?

Try Crystal Keep. I think they have a list by LA.

D&D 3.5e

Does anybody know of a way to have your armor change sizes when you do? Namely for a Therianthrope, specifically a were-bear.

Only way I know of is via Black Blood Hunter + Wilding clasps. Spell effects that enlarge you also enlarge your equipment for those times.

Black Blood Hunter?

Lycan PrC. Lets them treat their alt forms as wild shaping so that they can use wilding clasps. It's a 10 level PrC though, and you gain the ability at 5th level.

Though I think Beastskin armor will work for you.

Beastskin Armor requires spending a Wild Shape use to activate.

Ah. Forgot about that.

Personally, I would say yes to that. It's a class that lets you cast spells, and thus, is a spell-casting class.