Personally (in my limited experience, LOL!) I think it is more about personality than age as to whether your kids will get along.
I think you are doing a great thing by making sure you are really ready in yourself before having another one rather than just having another one at the wrong time because you think you should, KWIM? I have had so many moments of doubt both during pregnancy and after Phoebe was born, asking myself if I made a mistake by having them close together. We are getting by and things are getting easier but if circumstances had been different then I probably would've waited a bit longer.
Sometimes I think it'd be awesome if Natty was older and understood that I'd be able to give her more attention if she waited while I settled Phoebe to sleep... to have the older sibling able to understand that concept would be brilliant, LOL. And while hopefully my girls will be able to entertain themselves and play together before too long, there's no guarantee that they'll be into the same things anyway... they may have very different personalities.
Anyway, that was a long-winded way of saying I think you've made a great choice