My strategy right now is to sell the land to a real estate developer to develop the home at a steep discount ($150,000) but make a claim on the stake of the overall project to get my remaining money back, plus the profit of the build. 

Specifically, I'm looking for insights on:Finding a reliable hard money lender who can finance the entire purchase and rehab costs.Strategies to present this deal to the lender to increase the chances of approval.Any potential pitfalls or things to watch out for in the BRRRR process, especially given the foreclosure status of the property.Tips on managing the rehab while tenants are already in place.Thank you in advance for your help!

It will probably only get used during the winter. and I can see some maintenance issues too with all that moisture inside it would be easy to get mildew or mold growth started if it is not maintained properly and often. also it is traditional to follow up your time in the sauna with a dive into a nice cold lake (or pool), or at least you might want to have a cold outdoor shower nearby. personally I would spend my money on something like a hot tub before I bought a sauna.

I'm feeling like yes, having her reapply, seeing when her unemployment runs out, money in the bank, current job search status.

Let the money talk. 

Is there a financial vehicle where I can park that money and only pay taxes when I make withdrawals? 

You make more and more money over time.

I didn't implement it because I didn't feel comfortable setting up an official government-looking website and letterhead, tell them you will send them money to pay their taxes, then tell them that you can't.  

Depending on the location STR is going to make the most money because condo rentals are an attractive option due to the amenities.

The money is paid with receipts on the day of the tax sale.