Unless you are an attorney practicing real estate in the state of the subject property, the chances of reaching a wrong conclusion are too great and the consequences too costly.  

If you have enough funds in an IRA the alternative would be to establish a self-directed IRA, and have the IRA buy the property subject to existing financing (if your sister is willing to do that), you personally can't assume the mortgage b/c you are not allowed to provide a personal guarantee for IRA-owned property and have the IRA pay your sister for the equity.

However, this is subject to change, and some applications may take longer if they require additional review or if there are any issues or discrepancies that need to be addressed.As for tips to expedite the process, here are some general suggestions:Make sure your application is complete and accurate.

The LLC has no impact on the effective tax rates.Also if you acquire a property for the purpose of flipping, that will always be Ordinary Income, also likely subject to self-employment taxes.That particular sales event has no impact on the taxation of your normal rental income from other properties. 

You could do a subject to but I would be nervous about doing that on such a large deal when the bank has the right to call the loan.Great deal, though I don't know how I feel about making such an enormous profit off a church...

Even USFS leases are subject to sales.How certain do you feel that this lease will remain in place for the 30 years?

For extra formality, put it on a nice document with your letterhead.Re: Non-Binding Letter of Intent to Purchase Real Property Located at [Property Address]Dear [Recipient's Name]:This non-binding Letter of Intent ("LOI") is submitted by [Your Name] (the "Buyer") to [Recipient's Name] (the "Seller") with the intention of setting forth certain preliminary terms and conditions for the proposed acquisition of the real property located at [Property Address], inclusive of all improvements, appurtenances, and fixtures thereon (the "Property").Purchase PriceThe Buyer hereby proposes to purchase the Property for a total consideration of $[Amount] (the "Purchase Price"), which shall be subject to adjustment based on the results of the due diligence investigations and final negotiations.Earnest Money DepositContingent upon the execution of a definitive Purchase and Sale Agreement (the "PSA"), the Buyer shall deposit earnest money in the amount of $[Amount] (the "Earnest Money") into an escrow account designated by the mutual agreement of the parties.

I have a seller finance/subject to calculator that I am happy to share with you via email.

I say soft because it is subject to change once you order the appraisal and move forward with the UW process.

After a brief search, the IRS says-For tax years 2018 through 2025, if home equity loans or lines of credit secured by your main home or second home are used to buy, build, or substantially improve the residence, interest you pay on the borrowed funds is classified as home acquisition debt and may be deductible, subject to certain dollar limitations.