How much margin should I give myself for variation in rental income? 

It's (variations of):-"On average, ROUGHLY 50% of your rental income will be spent on expenses".Yes, properties that generate 2%+/m gross rental return are more likely to average HIGHER than 50% expenses (because risk / cap ex will be a higher PROPORTION of low purchase price).Conversely, properties that generate less than 1.25%/m gross rental return are more likely to average LESS than 50% expenses (ie. higher initial purchase price, but same cap ex $).

A large variation I found between my math and yours is the calculation of gross rents, and NOI.

I strongly believe automation in manufacturing is going to be catastrophic sooner rather than later and I need some variation in my portfolio. 

I know there are many different options to offer like interest only, 50/50 the whole deal, preferred percentage etc etc.I know this isn't a short and simple answer and there are different variations but for now im just trying to get a simple understanding 

There are numerous other pros/cons you can read through by searching BP for 'SFR vs Apartments' (or some variation).  

If the property was priced correctly when it went to market, there will not be a lot of variation.  

Sunriver is very picky about colors and styles, they want "natural" and it needs to fit in with existing homes, etc. which all have some variation of siding, windows have to be beige or gray, etc.

As far as flipping the homes I would be very very careful, extreme rural communities typically don’t have much price variations between 2 very different properties so can be hard to judge an accurate ARV and comps can be very difficulty for appraisers to find.

There are a million variations and things you could do with Sub2's which is one of the reasons why I love them.