It's hard to argue with simplicity. It looks like you chose a deep cycle which in my opinion would be the best thing to do if you're going with one battery. Deep cycles still have plenty of cranking power and you're one cylinder isn't going to draw a ton.
However I don't know that particular battery and the usual battery purchasing cautions apply: if you want a deep cycle, make sure it's really a deep cycle. Deep cycles will always have the 20 hour Ah rate marked on them. That said I know plenty of people around here go with Wal-Mart. If you have a Sam's Club nearby also consider this:
But also consider that you'll have no reserve bank should you leave a cabin light on and drain your one battery. Then you'll be stuck. One thing I considered with my 1 cylinder Yanmar was using a small $35 tractor battery as a reserve/start instead of a standard marine size one. You could consider that too if you wanted the usual reserve bank functionality but without much cost or weight.