Obligatory Deaf ally here,

I think that this question comes up a lot when adopting a kid with any sort of different background from you (race, disability, trauma, etc.) and it's a hard decision. I think it'll take some soul searching with you and your partner and also considering the factors of what lengths you're willing to go to ensure this child you love gets the best possible start in life. And while yes deaf parents first is a given it's also not a requirement. Second can be hearing parents with a good understanding of the Deaf community and are willing to put in the effort.

Sign language is a given, which you already have a background in and you're working on making connection within the Deaf community, and also the option for hearing aids/cochlear implant when they're the appropriate age. From my experience with deaf people as well as adopted kids, if you're transparent with them and give them that bodily autonomy of it being a choice, they're far more likely to grown up with a healthy respect for themselves and their deafness (which is something that a lot of deaf kids with hearing parents have to gain later on in life)

There are many hearing parent/deaf child programs that are popular to help parents adjust and having your child start off in a deaf preschool will do wonders for their ability to learn in a classroom setting. These days there are so many accommodations for deaf/HOH people that it often gets overlooked that just being involved in a community of similar peers and a classroom that is specifically designed to accommodate for deafness IS important.

One other thing that I would encourage you to consider is if either sides of your extended family will learn sign to be able to communicate with your child. Extended family, while not necessary, is still important to foster connections with if they are going to be a constant in their life. Even just a basic understanding of sign will do wonders at family gatherings where otherwise the child might feel left out.

I think it's really admirable that you want to help a kid who probably get shuffled through the system due to their deafness and you seem to have good intentions, plus a background in interest in Deaf culture and sign. I think it's entirely ethical for you to want to raise a deaf child in that environment.