There were 8 years between me and my brother and it worked fine. We couldn't have been described as "close" in that our interests were very different and in comparison to him I seemed adult no matter my age.
But I used to play with him and we would do games and Lego and even play on consoles together.
We weren't close while I was at uni and then while he was at uni but we have always been fond of each other.
Now we're both grown ups in work etc the gap seems much smaller.
I think you need to be aware of how your children are dealing with the blended family thing though, and be pretty wary of that.
I also ALWAYS had my own space. My bedroom was my room and it had a hook and eye on the door so I could shut my brother out. I wasn't allowed to be mean to him but he also wasn't allowed to bother me if I wanted to be on my own. I think that was a really really important thing in terms of our relationship working.
Similarly he would have had a fairly early bedtime for a decent while so me and my parents could watch a TV episode that wouldn't have been suitable.
I guess the big downside was I wasn't allowed many hobbies, and I did sometimes resent him for that, but it doesn't affect my relationship with him as an adult.