You may end up just buying the nipples your baby will take!
With my DD, I literally tried 12 different types of nipples from every brand and the Gerber NUK was the only type she'd take. Every manufacturer out there claims their nipples are "closest to the breast" but logic dictates that can't possibly be true
Now, many babies are prefectly fine with whatever nipple you start out with. Like I said, though, my DD wasn't one of those. Those orthodontic nipples (like the NUK and Playtex ortho), supposedly, are more like the breast because they aren't round, but rather squished and are shaped like a breast is when it baby's mouth. I don't know. . .but it's all my DD took. So all we could do is buy bottles that worked with those nipples.
Not all bottles work with all pumps. The Medela pumps all work with standard, narrow-necked bottles. If you're going to be using glass bottles, it'll work with the Evenflos. Any narrow-necked nipple will work with any standard narrow-necked bottle, so feel free to mix and match! In other words, find the nipple your LO prefers, then get whatever bottles you want that fits it. Doesn't have to be the same brand or anything.
Avents aren't a standard size and don't fit the Medela pumps directly, though there is an adapter you can purchase. Dr. Brown wide mouths don't fit anything else either, I don't think.
However, I will say that after a year of pumping for my DD, I really didn't find it that important as to whether the bottles fit on the pump or not. I just bought a few more narrow-necked bottles to pump in to, then transferred that milk into the bottles my DD would drink out of.