Seller financing is actually very common, and there's tons of info here on Bigger Pockets about it. 

No biggie, it’s fairly common.

Also see these:Real Estate WholesalingIntroduction to Real Estate Wholesaling | BiggerPockets Podcast #91The Ultimate Beginner’s Guide to Real Estate WholesalingA 60-Day Action Guide to Wholesaling Your First PropertyThe Newbie’s Guide to Wholesaling in 7 Simple StepsThe 8 Most Common Lies Newbies Believe About Wholesaling5 Costly Pitfalls That Catch Wholesaling Newbies Off GuardWholesaling CalculatorBest of luck to you!

The 50% rule is valid, and used by experienced investors for deal analysis because it works, and is surprisingly accurate across a wide spectrum of properties: https://www.biggerpockets.com/...It's common for listing agents to paint a rosy picture of a property's performance. 

While you can certainly send tenants an account statement, or notice showing what they owe, be very cautious about sending a pay or quit notice (we commonly call it a 3-day notice here in Florida), or any type of notice that mentions or threatens eviction. 

If it says they cannot leave things in the common areas, do it.  

They will definitely have one for July 4th and they have them very commonly.

If this is the only capital you have access to, option 1 may be preferable, since that leaves you with some available capital should an emergency arise.

We had one in our SFR for 12 years & reglazing was a common reoccurrence.

We don't yet have the density issues that other cities like Portland (where ADU's are quite common) have.