If you’re over the $500k gain, congrats, but you would probably still be better off just renting the home for a year or 2 and exchanging the part over $500k instead of building an du just for that purpose. 

I've created several LLCs for different purposes (coaching business, rental business, etc.) very quickly and easily myself through my state's secretary of state website.

You can set up a management company if there's a purpose, such as generating qualifying SE income to fund retirement accounts and such/I highly recommend working with a REI tax strategist to make sure both of these are appropiately setup.

My circumstances are as you describe, and I got the study done, am a real estate professional for tax purposes, while hubby has the W-2.  

LLCs are great for branding purposes, organization and offer real protection.

I would guess that the stain is the result of steel or maybe cast iron pan in contact with wet wood. 

YMMV (your mileage may vary)Fixable alone: boiler maintenance and steam system rebalancing, minor lead paint sealing, plaster patching (even very large ones), thermostat installation, insulate flooring and rim joists, painting, floor repair, skim coating walls, installing thresholds, weatherproofing, installing/refinishing door and cabinet hardware, adjuster gutter drainageNeeded professionals: sewage main unclogging ($), knob and tube disconnection+removal ($$), flooring ($$), adding joists for structural support within walls ($$), replacement and removal of old brass/cast iron plumbing where necessary ($$$), new gas line for laundry and lines for appliances ($), wall demo + replacement ($$$), steam line moving and radiator repair ($$), gutters ($$)$ - hundreds, $$ - thousands, $$$ 5K-10K, $$$$ - tens of thousandsHope this helps, best of luck with the old home!

The follow-up email included the PM's address for registration purposes for any formation of an in-state LLC (not sure that was a recommendation as it was not explicit in the follow-up, but Morris has advocated for this in his podcast). 

It does not allow me to use the funds for the purpose of investing in real estate property. 

they will be able to point you in the right direction of all the things you need to do for tax purposes.