Sibling age gap - What's best?

Okay, so this has been on my mind for a few weeks now... I've thinking a lot about the ideal time between babies. And, No! I'm not pregnant or wanting to be right now! Just thinking.

We know we want to have another child at some point, but the question is, when? And I know you can't always plan things perfectly but when should we even aim to start trying again?

Lila is nearing her first birthday and I'd love for her to have a brother or sister relatively close to her age. My brother is 2.5 years younger than me and although we tormented each other at times we have gotten along pretty well our whole lives. From what I hear, 2-3 years apart is pretty ideal.

My hopes with the spacing:

- The kids can play together well

- Lila kind of knows what is going on when the new baby comes

- Lila is potty trained or close to it when we have a newborn

- The kids will both attend the same schools some of the time: 1st and 4th grade, or freshman and senior

I'd also like to avoid a June - October baby because of work reasons (my busiest time is August - October). And again, I know this is hard to plan. But ideally, I'd like a winter or spring baby.

So that said, is 2.5 years apart the best? Is 3.5 too much? Is there really much of a difference? Does it have more to do with the older child's temperament than age?

Let's just say we achieve a 2.5 year age gap exactly. Lila will be 2.5 on August 23, 2013. Since I'd like to avoid that time of year to have a baby it will probably be sooner than that. Or later?

An April 2013 baby would make the kiddos 26 months apart. Is that too close? And I'd need to be pregnant again this coming July! Am I even ready for that?! Since I'm absolutely terrified to go into labor again...Methinks... NO.

A little bit over a 3 year age gap would be April or May of 2014. Lila will likely be potty trained by then and old enough to kind of know what's going on. But if we aim for that time, what if it takes us awhile to get pregnant? It's not the end of the world but would a 4 year age gap be too much?

What I'm thinking now is trying for another baby right around Lila's 2nd birthday in February of 2013. Hopefully I'll be pregnant before summer and will be having a baby in late Fall 2013 or Winter/Spring of 2014. On the early end that'd be an October baby and Lila would be a bit over 2.5. On the later end, she'd get a sibling right after her 3rd birthday.

The only downside I see to this is that I'd be pregnant on my 30th birthday in September 2013! I totally wanted to be in Vegas or on a cruise!

It helped to think that out "on paper"... but in the end I know you can't always plan things like this. I guess we will know when we are ready to add to our family and it will happen when it happens! Anyone have any insights into the best sibling age gap?