Hello,
My LO is 2 weeks old and I pumped this morning for the first time to start a stash. What size portions do you freeze? I pumped 4oz. Should I freeze two 2oz servings. How much do they eat now at each feeding and how does that increase over time? I don't want to waste freezer bags with tiny portions but don't want to waste milk with big portions. Can I thaw more than one bag and combine them in the same bottle if I have 2oz bags and she eats 4 at a time?? Thanks.
Re: portion size to freeze
For now I would freeze 2oz at a time since your LO isn't eating much yet. In a few weeks you'll notice LO eating more and you can make bigger bags with 4oz etc.
As for thawing. You can combine different thawed bags into the same bottle.
Thats actually a good idea. TWICE, yes TWICE I had the Lanisoh bags with 5 oz. each
leak. I didn't realize there was an issue until I tried thawing them 
This exactly. Better to "waste" bags for now but then later you will realize you can do bigger bags. Almost all moms would rather waste bags than milk.
As for building a stash in general--this is a good idea, but don't go overboard with it. In theory you don't need to build a stash that's more than a day long, because you'll be pumping what LO will have for the next day. You don't want too much of an oversupply. But an itty bitty oversupply is never a bad thing. Milk will get spilled, you might need to travel for longer, etc.
The other problem with building too large of a stash is if anything happens to your power (especially now that it's winter) you could lose the whole thing. It's one thing to lose 20oz or so, it's completely another to lose 200 oz.
I freeze in 5 oz increments because she was fed from 2.5 oz bottles. That way we could thaw and have two bottles. Anytime I'd leave it was usually for two feedings (I'm a SAHM so it was just for running errands alone, going out with friends, or date night) so that worked well for us.
Now my LO is rejecting bottles though so I don't bother pumping. I have about a day worth of milk (30 oz) in the freezer just in case something happened.