I understand your thinking, parenting a child with health issues (mental and/or physical) is tough, but it is just one of the possibilities we sign up for when we have children (be they bio or adopted). Bringing a child who is likely to have such issues into the world is a completely different consideration.
I would say that the 'risk' that your child will have issues of one kind or another is highest if you adopt. If you conceive a bio child, yes there are chances that you pass on genetic susceptibilities, but conception is a real mix up of the genes, so equally chances are your child would not have any bad genes. Also, your birth child may inherit genetic dispositions e.g. towards depression, but never have those dispositions triggered.
Whereas for the child you adopt, it is not really a matter of 'if', but only of 'how much'.
So choosing to create your family by adoption is the path that is more likely to lead to 'special' parenting. I think it is important to understand that. But I get that your point is about bringing someone with issues into the world, vs a child that is already there.
I would also like to point out that some part of family transmission of things e.g. depression is not about genes. If the primary care giver is not emotionally available, because they are dealing with their own depression, the child is more likely to develop depression as well. Adopting a child does not insure you against passing on certain issues, you might just be passing them on by different means than by genes.
When talking to adoption agencies (and when considering things and doing your own research) I think it is important to consider if /how far your experience of your issues is a strength (you are aware, can recognise, know how to deal with/manage, don't stigmatize, can support, can empathise, have mechanisms of support set up for your bad times) and how much it remains a liability (adoption is emotionally draining, will it take more than you can give? Will you be able to remain emotionally available? What if an important period of your child's life falls into a 'bad time' of yours?)
Overall I feel your reasoning is ok. You want children, and are aware that whenever you have children, whichever way you go about it, there is a risk that they have or develop some sort of 'issue'; but you don't want to bring a child into the world who would suffer like you do.
There are lots of reasons why people adopt. They usually start with 'We want to have a child' but all the rest is highly individual. Why not go along to an adoption information evening and start finding out more?
But bear in mind that many people who want to have a child don't get there by their first choice of 'means' (and sometimes not at all). Many would like to have a birth child but can't, and turn to adoption as second or third choice after exhausting other possibilities. Some (a minority) would like to adopt, but can't, and turn to conceiving a birth child as second or third choice. Just remember that there are factors at play outside of your control.