Often a development will need to disturb or destroy some habitat onsite simply to get a workable footprint.

I simply would not risk a family vacation on this type of lodging.. plus you don't get any points..

You can certainly simply make payments for your parents as a gift.

If the sunroom is already appropriately permitted and a legal addition then converting the use in the property doesn't require permitting if you are simply repairing the distress. 

If you have old wooden windows, the lead inspector won't bother to take swabs, they'll simply fail you for old wooden (friction) windows.

Once the account is set up and funded through either: a transfer, a rollover or a contribution (or mix of those things) they simply follow the custodian/administrators process for investing.

You may want to look into more turnkey investments where you can invest $1M of equity in a more stable asset class and target a cap rate of 7%+ and simply hire someone to manage the investment for you. 

I never had a C-corp before so I don't know, Can i simply assign interest in the property holding LLC out of my C-corp and to my main holding company. 

You might start by simply looking at the history of the homes you've worked on over the last 5 years.

There are pros and additional risk taken when entering a subject-to.