D.W.
First of all, congratulations!
Your baby will dictate what kind of bottle they like. Dr. Brown's didn't really reduce the gas in my kids despite being recommended by our pediatrician. As a working mom, I found them to have too many steps to wash to make it practical.
With our son, we had a lady come to our house to watch him, but we moved the kids to day care once our daughter was born, and the state laws regarding milk are much more stringent. We had up to 6 bottles/day at some times depending on her appetite, and we had to hand wash them each day because of the practicality of running the dishwasher that frequently.
Our kids both took well to Avent and Platex Drop Ins (Dr. Browns was another they took to well, but we did have some issues with leaking).
Breast milk and formula is very fatty, so you'll have to have some kind of detergent to break down the fat content to wash them. I found hand washing to be easiest though annoying at 10:30 each night. I also found preparing bottles the night before was much easier, but our state laws require they be used within 24 hours, so I'd do it right before going to bed.
Check with your day care provider to find out what they'll allow you to do. Ours required bottles all be made in advance because of the time component. Anything not consumed within an hour of initial feeding had to be thrown away, and they keep strict charts.
I'd recommend waiting before opening your pump. Once it's open, it can't be returned. I've not known anyone to use an Avent because Medela is the market leader by far - a lot of hospitals and pharmacies have pumps for rent to help you select the one that works best for you. It's an expensive investment to perhaps not like.
Good luck!