I have 13 months between my two which was not entirely planned or unplanned. Yes, it is exhausting working while pregnant and with another infant to care for, but it does pay dividends further down the line. My eldest can't remember it ever just being him and we never really had the jealousy thing going at all - except for the occasional spats - but you will find that there is room on your knee for two. I do sometimes think that they both never really had the time to be babies. But, i think that they gained so much more from growing up together. I am lucky that my two boys are friends and share similar interests and sense of humour - I hope they stay close as they grow into adulthood (they are 10 and 9 now).
I don't think there is an ideal gap, you just do what you need to do and what suits one person doesn't suit another - remember that their personality will also have a bearing on what works, but by the time you know that, it's usually too late! I have a friend who has two girls with a similar gap to mine and they never got along and still don't at 16 and 15.
I'd just go for it.