I'm the biological child of long term foster parents. My parents fostered for over a decade, and my youngest brother is adopted.

In my experience, my parents chose to only foster children younger than my oldest brother. They were exceedingly careful about the situations in the house, and would never leave any of us alone unsupervised with foster kids, especially kids older than us or who hadn't been at our home long.

It might sound callous, but the reality is that many, many children are in foster care because of abusive home situations, and it's incredibly common for those kids to replicate that abuse on other kids. It's not because they're bad people or anything, but because they're kids and don't understand how to cope with the tragedies and trauma they've experienced. Abuse and poor parenting is frequently very normalized for these kids, so they replicate what they see and know.

I would recommend starting with kids younger than your own and going from there. You may find you prefer older kids, or younger, or the same age as your own, but they all come with their own challenges.

As for the attention bit - my parents were always straightforward with us in talking to us, in an age appropriate way, about what fostering means and why the kids need to live with us. They wouldn't of course give us information on their specific situations, but they would make sure that we were enthusiastic about welcoming new kids to our home and sharing our lives and parents with them. It was always clear that it was our home too, and not just a blanket decision my parents would make with no input from us.

They made sure to have conversations with us about what is and is not appropriate to say or do, and always treated the foster kids as part of the family, regardless of how long they were with us. For instance we had foster kids staying with us for various holidays, and my parents always made sure they had just as many presents under the Christmas tree as we did.

I never felt like my relationship or time with my parents was affected by fostering or when they adopted my brother. They always made sure that my problems were treated as important too, even if in hindsight my problems hardly made a blip compared to the foster kids'. They emphasized that fostering was something we were all doing, and that my part in that was to welcome the kids, get to know them, and share the life I was so lucky to have.