I can tell you that from my personal experiences, Mt. Pleasant is not an area that is making a change to even a C. Slavic Village is interesting as Newburgh Heights is an area that is now C in areas, but once you come more towards the Broadway area it gets rough. I actually am rooting for Slavic Village as it has some potential for sure, so if you want to be an early developer then this might be something to look into. But know that North Broadway and the surrounding areas have some of the highest crime rates in the city proper.
Now from someone who knows Cleveland's vouchers (sort of), the bigger ones are Section 8, EDEN, and Parma Public Housing Assistance.
Last remark, I really like Lorain and possibly Elyria if you're looking for Section 8/EDEN rentals. Lots of good PMs that manage there, not too rough of an area for the price, and a lot of voucher demand from my experience.
Reach out if there's anything else I can help with! Thanks.