Good Morning~ As your little one grows, she's going to get a bigger appetite. I think buying larger bottles will be a good investment. My daughter is a pig, but when I feed her out of the 6 oz playtex bottle vs. the 8 oz Dr. Brown's bottle, she gets mad at me because the last 2 oz aren't there. I absolutely love the Dr. Brown's bottles. They're a different design and have more pieces, but it's much better than dealing with a plastic liner. If you get them, you might want to invest in the container that goes in the dishwasher (if you have one)that holds all the pieces. We just got a dishwasher and it saves so much time trying to clean all the bottles and parts. Also, because your daughter is almost 6 months, think about step 2 nipples vs. step 1. Step 2 nipples are just a little bigger and as her appetite increases, it'll make it easier for her to pull the substance in and not have to try so hard.
Don't freak out about the specific amount she's eating and calculating that the total fits in whatever she's "supposed" to eat. All of the "supposed" to's can drive you crazy and the fact is as long as she's eating, healthy, and gaining size everything is ok.
Regarding what to buy innitially: First, I started Taylor off with Stage 1 food at 4 mos. A lot of moms disagree with starting them off with food before 6 mos- 1 yr, but she needed more than formula or breast milk to satisfy her. It's all about your child, not what everyone else's child did. It is so fun introducing your little one to new tastes and experiences. I've had a ball over the last 4-5 months with the stage 1 snacks (some dissolve, so there's less chance of choking) AND it's been a huge help to tide my monster over until I can get her bottle or food ready. Buy one grain cereal or oatmeal. As long as it's one grain, her little digestive system can handle it. Obviously, I started with Stage 1 food, but I quickly changed to stage 2 food because of Taylor's appetite. Stage 2 is generally just bigger containers. While in Stage 1 foods, I would mix some of the single grain rice cereal/oatmeal with the stage 1 food and microwave it for like 10-15 seconds. She LOVED it.
She's 9 months old today and insists she eat off of my plate (not for a complete meal, though). Of course, I either give her mashed potatoes, small pasta, or mush up whatever else, but just watching her face with new tastes is so exciting!
Soak up the time you spend with her especially in the next few months because everything is new and exciting and it'll make you feel like a kid again (with a mortgage :)
E.