In the meantime use the search function on BP and type in lifestyles Unlimited  and I think there are some post from the past of similar questions. 

I’d love to hear from anyone familiar with the rental market in El Cajon or who has built/rented ADUs in similar areas.

Similarly, if you put all Class D tenants in a Class A 4-plex, what do you think will happen?

A few things to keep in mind:Section 8 requires the property to pass an inspection based on HUD’s Housing Quality Standards (basically making sure it’s safe and well-maintained).The rent you charge has to align with Fair Market Rents (FMRs) in your area, so it’s good to check what similar properties are renting for.You’ll still be responsible for maintaining the property, but the upside is that a chunk of the rent is guaranteed by the government, which can provide steady income.Check with the local housing authority about any specifics for your area—every jurisdiction does things a little differently.This could be a great niche if you can find a good deal on the land and make sure your expenses (like maintenance, insurance, and occasional vacancies) are covered by the rental income.

I bought nothing.2021 was similar, but prices got silly.

I work as a part-time CFO for several real estate developers like yourself and help them through similar challenging times.

Similarly, if you put all Class D tenants in a Class A 4-plex, what do you think will happen?

Once you find a lender that finances properties similar to yours, start building a relationship.

If the comps pulled are selling between 280-290k and are very similar, should I be concerned with the end goal of this deal? 

I'm in a similar situation and am curious about what you did.