We just added on 500 sq ft, and it turned out to cost less (up front and long term) to put a mini-split in the addition, rather than add ducts and zoning.

It automatically sends follow up emails thanking them for attending my open house with additional information on how I can better serve them. 

If you're about being the most efficient with insurance costs and cant cash flow the full annual premium up front, you may want to consider escrowing for the additional discount(s).

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.

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.