It wouldn't be a bad idea to get a second opinion, either from a GC you trust, or from a home inspector. 

What left  a bad tase in my mouth?       

You need an oscillator really bad. 99 bucks for the tool. 

Then folks who are hanging out in the kitchen or living room on the main floor would have the choice of using either the upstairs shared bath or the downstairs shared bath.Are you certain there's no way to create a half-bath on the main floor?

If you believe that things are as they always will be, (first you should look at the past and see if that is a reasonable assessment of what the future brings) then taking into account: limitations on what you can invest in, your Solo 401(k) "projected" growth, fees & hidden fees, you can't co-mingle funds, you have to carefully manage the process, future tax increases, tax law changes, a national debt that is north of $22 Trillion dollars, unfunded liabilities and and of course inflation, along with possible "bail ins" then you are well equipped to decide if that is a good choice for your style of investing.However, If you are an "opportunistic investor" . . . . you jump at the opportunity when it arises, then you run into some conflicts.

Now, is that a good thing or a bad thing?

Assuming the price is exactly the same between your quotes - If I was you I would be looking for the best possible coverage amount / settlement terms for the price paid.Also once you think you have a final choice selected - make sure the numbers you are looking at are the real numbers and not what I call shopping numbers that then go to underwriting for review after the policy is issued.

Home Inspections (while important), can be pretty bad at catching major issues.

Your way doesn't sound bad or good.

They already have relationships with trusted contractors, leasing agents, and some have property management in-house.BRRRR can be a good choice, but it all depends on how much time you have to dedicate to the project, and how far away you are located.