I was paid nearly double what I charge to manage in the suburbs but it's not worth the hassle. 

I ask because I was running numbers on a demi-detached here in MD and although the cash flow made sense to me (50% of total amount) but the cash on cash ROI was not in double digits.

Whatever is making you money right now double down on that and scale it while the market is hot.

If that number hits double digits it could get a bit sketchier.

Installing sound batt insulation between floor joists. 2.Hanging ceiling drywall underneath a layer of vinyl and a firing strip.If that is not an option then some options would be to install a double layer floor like in picture number 2.

Say they can either have 110k in cash now, 125k if I give you 10% down, pay you 4% annual interest(double what bank will give you in savings account) only paid out monthly, balloon in 2 years(promise to cash you out) or 150k with 0% down 4% interest amortized over 30 years.

Those who are already wealthy and want to preserve what they already have in a safer way are happy to double to triple outpace inflation annually they just do not want lots of their capital at risk.This is very different from a much younger and opportunistic investor still trying to create wealth and taking higher risk strategies.   

I assumed everyone would answer  as I know value is driven by amenities, size of unit, and location of unit but just wanted to double check before I start a plan of what to do. 

i have a house that has almost doubled in value while covering my mortgage by renting out my garage unit.

Taking the 30-year option will allow you to double your cash flow allowing you to scale faster.As long as you have a positive cash flow on the property it shouldn't negatively impact your DTI.If your goal is to continue with the property you have then I think the 15-year may be a good option.