I have two younger half sisters (4 & 6 year gaps) and a half brother who is 10 years younger. We don't have the same dad (they do) but it makes no difference, I adored them growing up, we fought like siblings when they reached teens but we share 'in jokes', experiences, a lot of history and I can't imagine life without them. Dh has two brothers, a half brother on his dads side and two step sisters, so we both come from big families that way. I always wanted 4 but the practicality and expense means we'll stop with my son and daughter (18 month age gap).
They annoy each other, snatch, fight, yell at times but they cuddle, kiss, she idolises her big brother and shes his babs and it works great. Shes brought my son out of his shell in public and its easy to see they're learning from each other. I didn't imagine it'd be as hard at times but then I'd not change a thing we did. The thing that has been most difficult was splitting my attention. Its doable but more than two I don't think I'd manage well.
Good luck with whatever you decide. We got a shock with my daughter so wasn't totally planned at that time but works so well for us x