My battery of choice is usually 1300mAh, but I also run a 1500. It depends on what else I'm flying that day as I have two of each of those sizes and I might need one of those sizes for the other planes. With my setup the 1500 balances it out nicely, but the 1300 needs a pair of washers in the nose for the extra weight. The 1800 is possible, but you may have problems getting it through the battery hatch.
As you're building it, keep in mind that putting the elevator and rudder servos in the tail (like I did) can determine if you need nose weight or not for balance. The plane is designed for installing them at the tail or under the wing, a nice touch by MM. You'll be very impressed with how well it goes together. For me, the hardest part of the build was the battery hatch. I should have assembled it with TiteBond II (or similar slower setting glue) and then put it flat on a building board with some weight on top of it. This would make the top sheeting curve and keep the bottom flat. Mine wasn't curved enough so it doesn't fit quite right. Not a huge issue though.
The ACE is a great example of a "Stick", and probably one of the easiest-to-build balsa Sticks you could ever hope for. Heck, it's probably one of the easiest-to-build balsa planes you could find in general. Mine is the first balsa plane I ever built. I was afraid to fly it (I had very limited stick-time when it was completed) so I built and flew the MM Switchback to build some skills. When flying the ACE I found it was much easier to fly (with low rates) than I had expected. Please post updates as you build!