We have a big age gap. My first got lots of 1-1 time with me, my second is now getting lots of 1-1 time with me when eldest is at school. My eldest loves being a big sis, and it is awesome to watch her playing with baby and showing her toys, reading to her--and it makes baby care very very relaxing and easy for me. No fighting, jealousy or competition. They adopt different roles in the family, basically.
The downsides are that you spread your childrearing years over more years and get to be an empty nester later, and career wise, you do have a couple more years with your work stuff on the back burner. In areas which are car-dependent, I think it could be tough having to cart kids around to different things (this is not an issue for us though as I live in a country where we have good PT and older kids/teens are expected to get themselves here and there).
All in all, I like having a big age gap.
As adults, intra-sibling relationships are mainly about how similar their personalities are IME, not about how close they are in age. Siblings with dissimilar characters usually grow apart as they get older even if they played together a lot as kids. Other siblings get closer as they got older, even if they were born years apart, if their personalities and interests are aligned. It's mostly luck of the draw, I think--never have kids assuming they will be best buddies in the long term, because this is very hard to control.
Don't worry, seriously. Kids do great with all kinds of family setups and structures.