You won't be unable to change it if you start with the smaller size opening...right? Try it...your instincts and what you've learned from reading seem 'on the money'. When the colony gets bigger, it'll be appropriate to give them a larger opening.
Does it cover the whole inner cover hole or are you giving them a nice place to build some of the drone comb they've been wanting to build.I doubted whether or not I was going to remove the darn feeder so many times that I ended up upturning the mason jar on the inner cover over the hole in the center, placing a super on top of that to protect it, and being done with it. An alternative to the feeder idea on scientificbeekeeping only I didn't have to cut my own board by using the inner cover. I'm sure I've seen someone else do that anyway...I digress...Out of sight, out of mind, right? Oh internet, how you help uneasy Newbs publicize their indecisiveness.
On another note, I'm totally using the entrance bases to supply water! Quick, someone give Rusty a cookie. Great idea.