Do I need starter for 2.5 gal batch?

What's the gravity of the wort?

But yes, if you have already determined that 2 packs would give you enough cells for 5 gallons, then linear scaling (down) is appropriate.

 

I've also read that making a starter with dry yeast is not recommended. Not sure if this is settled.

For the times I've used dry I always just re-hydrated per the directions.

 

I've made starters out of dry yeast plenty of times with good results.

I say always make a starter if you can. No, not necessary, but never a bad thing...

 

If your dry yeast is an 11.5 gram pack, I'd say you're probably good to go.

 

Never lagered and know nothing about it, so forgive my ignorance here. Does it take twice as much lager yeast to ferment a 5 gallon batch with this as the OG? One packet of ale yeast (starter or no starter) would take care of a 5 gallon batch with that OG, no problem...

 

Ideally, lagers take more yeast than ales. Opinions vary about how much more, but 100% more is a pretty common rule.