We have had a Strctural Engineer out to the property and while we don't need to conduct repairs within the next 5 years or so, we will need to address both of these things at some point and it will likely cost us about 100k.Any advice on selling or holding for the long term?

They are your stereotypical ‘salesman’ type brokers, more about just selling any and all homes than they are studying the markets.

You can track materials used to fill in your JIT processes or whatever.With a vacation rental, it is always different.

If you proceed with the project, you should go through the proper permitting process.

I've dabbled in the new construction space here in Chicago and there is A LOT that goes into it...I'd highly suggest spending some 1:1 time networking with some other investors like @Jennie Berger or @Prashanth Mahakali who are both Chicago developersYou make your money with the land purchase and then systems/processes/volume over time in the development game, but it's not easy and competition is high!

I am wanting to invest 100% into real-estate whether it is flip and sell and/or long term rentals. 

Tried hand at seller financing but they just want to sell and retire. 

We usually had around 3 other people renting for us and sold the house a few years later as the largest sell price in that neighborhood to that date.

The crazy thing was that we didn’t lose cash flow by doing this because the mortgage pay down reduced more expenses than we lost in income from selling the properties!

If the owner is going to buy and sell their properties with us than we don't charge anything for any renovation.