This is what I registered for and ended up loving. Breastfeeding didn't work out for us so we had to use formula. I like that you can hear the vents working so your LO gets less air and ideally won't have problems with gas. They're also really easy to take apart and clean (i wanted to try dr. brown but heard a lot of negatives about all of the tiny parts and cleaning).
As for the size question, you're totally right. We got a few 4oz bottles and a few 8oz bottles and really could have just used the larger ones the whole time. The only thing you want to look for is "nipple speed." The smaller bottles tend to come with a slower nipple and the larger ones come with faster nipples, but I'm sure you could buy several large bottles and get the nipples separately. Depending on the brand they're either marked "slow/fast," "stage 1/stage 2," or something along those lines.