However with your first point that would be the same whether our next child is biological (not that we can have anymore) or adopted. Those feelings in the first child can feel would be the same adding a child to the family
As @121Sarah said, there are key differences in adoption you need to consider.
If you were to have another birth child your child would have the time over the pregnancy to start to adjust to being a sibling, they’d see your pregnancy progress, see scan pictures, look out their old baby stuff etc etc, and even with that preparation and inclusion might feel jealous or displaced.
In adoption much of that process isn’t visible or seen, depending on age your little one might have really limited understanding of adoption and won’t have the preparation process that comes with pregnancy. It’s a hard adjustment fir adults to bring home this fully formed child and start bonding, claiming the child as their own - and they’ve had some control in the process.
The child you adopt will likely need a lot of care, much more than a birth child of the same stage and you don’t have birth hormones to help with that bonding process. Your little one may not be able to help with the care of your new child in the way they might with a birth sibling, because the adopted child needs to come to you and your partner for caregiving, and having an older sibling provide care might echo a previous sibling relationship and retraumatise it confuse the new child.
It’s a completely different way of adding to your family and you will have lots of competing priorities with both children - many more than with two birth children. From a very practical point of view having separate space for each child is vital when you just need to deal with the one in front of you and the other can be safe in their room.
You won’t be approved without having a separate bedroom for the adopted child, you can certainly start the process but the expectation would be that they both have their own space, even if your adopted child is in with you initially.