Have seen some on older threads but if there are additional recommendations would be much appreciated.

In addition, I’d recommend going to real estate investment meetings in your area, making friends, and exchanging work for knowledge (or some similar arrangement) so that you can supercharge your skills without taking too much risk (see the BiggerPockets Events page, or google the topic).

That 10,000 additional is his "interest" and if you want to calculate a rate on that then great but just keep it simple.1.

I wouldn't put too much weight on what grade it has per the county website, as that is pretty general. 

The investment property clears about $800/month.Does anyone have guidance on how I may tap into my equity for additional investments? 

He would either put up all the capital for the purchase & renovation, or he would provide the initial capital and the additional financing. 

I saw that you said the property manager has a lot of experience with turning units to get them reno’d so maybe the additional 6 months to a year of rental premiums could be your hedge on that $50k in repairs that needs to be completed, as long as it makes sense for you guys.

I set aside 8% per month for vacancy in addition to 5% cap-ex, 5% maintenance, 10% PM (which they take directly), etc.  

(My husband has another full time job in addition to flipping). 

In GA (if that's where you're looking in invest), after winning an auction you are issued a "Redeemable Deed" that, if the property owner redeems, the winning bidder is paid back their investment amount, plus 20% penalty on the first year of elapsed taxes, and 10% on any additional year after.