Re: 4+ gap
The older of my two brothers is only 13 months younger than me. But the youngest is 5.5 years younger. My youngest brother used to feel left out when he was little. Now my two brothers are very close.
2-5 year age gap seems pretty common in my family. I see a lot of 3-4 year gaps in the more recent generation.
Hubby and his older brother are 4 years apart. Their younger sis is 12 years younger than hubby (and 16 years younger than the older bro!). Hubby was picked on a lot by his older bro when he was little. Now his older brother is much more caring and kind (and was especially attentive to his little sis).
The one thing I've noticed is that with a gap of 4+ years, children tend to socialize a lot more with people outside of their home. That's in general not a bad thing, but I do notice that in my family, a lot of those kids tend to be the ones that, as they get older, "stray" from the values that their parents have and are more invested in being like their friends. So it's just something to be aware of and keep in mind as you raise them.