I'm just back of napkin, this is what's out there - Stated income (no personal), LLC no problem, 30 day seasoning to 70 ltv. 30 year amortization.

I’m under contract with a property in Cleveland in the Linndale section that has sewer or sanitary line issues.

Is it best to do 'napkin' style informal or more thorough? 

Sure, for paper napkin formulas, these could be a quick way to discriminate deals, but what it lacks is the thoughtful process behind it, the ability to zoom out to a greater context. 

However, there is a basic "back of the napkin" evaluation that will usually tell you if the deal is worth a closer look.

We will be living on the house for 3 years, we can not have roommates since my son is immunocompromised and he can get sick super fast, and is hard to force strangers to comply with all the required sanitary procedures to live with us.We want some equity, and we will like to learn the real estate business so we can do this once we get out the current situation.Thank you

Use the 2% rule on the back of a napkin.

What they are producing is akin to "I own this property, signed bogus BIG BANK President, Vice President, etc." on the back of a bar napkin and expecting it to be legal and prove their ownership.

YOU MUST keep good records and make sure you have hard numbers on the repairs, not a napkin faced "guesstimate".

You need to know about flood plains, platting, topography mapping, road design, drainage design, water distribution systems and design, coordinate with utility companies, construction staking and final lot staking.You need to have an environemntal site assessment from a geotechnical firm, find out about any and all impact fees and permit fees, and possibly off site drainage improvements, off-site sanitary sewer extension, & on & off site water pressure measurements from the fire department to the hydrants.