i have read some opinions on NOT aerating the wort if using dry yeast. That sounded off to me, but i've seen it a few times.
I've seen them too, but without sufficient reasoning or better, facts, it doesn't sound right to me either.
Back in the days is was thought that an 11.5 gram pouch of dry yeast contained an abundance of cells, as much as 200-300 billion, a royal pitch and much growth was not needed. Even if half of them didn't make it, due to osmotic pressure when sprinkling dry onto the batch's surface, there would still be plenty left. Plus the cells had more than adequate sterol reserves built up before being dried.
That number of cells in a dry yeast pouch has been debunked, 65-90 (?) billion cells seemed to be the average depending on the strain, but the associated need to aerate/oxygenate for replication (budding, needing healthy cell walls) was never addressed, AFAIK.
Should one aerate with dry just as with liquid?
I don't think aeration/oxygenation will hurt, it may even help. I would!
I've always aerated as much as I could (shaking, whisking), and only had one stalled batch. That was a 1.090 Old Ale using 2 packs of rehydrated S-04 in 5 gallons, finishing at 1.030. It wouldn't budge, tried for 2 weeks, nothing fixed it. A small temp drop overnight may have been the culprit, although I'm not sure what the real issue was.
Later I started using pure oxygen, but haven't used dry yeast since then.
Also... if i wanted to use one pack of a dry lager yeast, can i make a 2L starter just as if with liquid?
Yes, why not?
If you want to rehydrate the yeast first, do so in half a liter (?) of 90F water, per the yeast manufacturers instructions, in the starter flask. When rehydrated, add 1.5 liter of, chilled to room temps, 1.053 starter wort to it. That will bring it close to 1.040.
I make starter wort in a stainless pot. Chilled in the sink or tub with cold water.
Don't forget to add a drop of Fermcap.