What type of foundation is it?

Being in your 30s you have the time to pay off that type of property. 

Welcome Abbas,What type of REI are you looking to focus on?

If a beginner buys TDs as described in this post, and they yield 10.5%, what type of losses should be expected over the long run? 

That seems logical - The way a seller financning transaction "should" go is the same as any other type of financing.

The fee structure in PM is so complex just looking at other companies and my own lolIt would be nice simplifying it from a consumer standpoint.We rolled out a monthly flat fee and thus far investors like it.Might completely transition to this model eventually.But all in all PM's have so many different fee structures for the various markets, asset and property types 

I'm looking to pivot into that type of strategy here soon! 

Just read some actual real life publications of this happening in the San Bernadino County California so this type of project is definitely possible.

I've been doing BRRRR type deals in the midwest for the last few years.

Here's a list to give you an idea:Startup Costs:Down PaymentClosing CostsProperty InspectionAppraisal FeeProperty InsuranceInitial Repairs and RenovationsEmergency FundOngoing Expenses:Mortgage PaymentsProperty TaxesUtilitiesProperty Management FeesInsurance PremiumsMaintenance and RepairsVacancy CostsProperty DepreciationLegal and Accounting FeesRemember that these costs can vary based on factors like location, property type, and personal preferences.