He has his preferred vendors, but you can continue to use your own brokerage with no connection to him if you are so inclined. 

Any chance for a vendor take back mortgage?

Does their contract require you use their vendors?

Payments are to be handled by outside/3rd party escrow (mortgage, taxes, insurance, etc), vendor to be determined prior to close of this escrow.  

Perhaps this agent and vendor are ready to be creative, as 3 years is a long time to carry property with no income.If you have any specific questions about owner financing, feel free to contact me, I've done a number of deals like this on the private market. 

To find and coordinate different vendors for different tasks and trusting it will get done, then not having the time to deal with what comes when a repair or service goes wrong.

Unpaid vendor liens?

Home insurance won't cover a lot of system failures like electrical.Home warranties are designed to make the warranty provider money; they are slow to respond, quick to reject claims, charge you a trip fee for every visit, use the lowest-cost vendors that provide quick-fix solutions, and are generally not worth the paper they are written on.

They can ACH it, walk in to a branch with cash or a personal check, etc.I know a lot of people find these third party vendors convenient, but to me it just puts another link in the chain between the tenant's payment and my revenue. 

Perform the same task in each app to ensure a fair comparison.Load a property with pictures and details.Market that property.See what your marketing looks like from the public's perspective.Submit a fake application to see how easy the process is.Run a credit/screening report on yourself.Enter a maintenance request, assign a vendor, and attach a fake invoice.Enter charges to the tenant's ledger.Enter recurring charges and automatic late fees.Sign documents electronically.Run owner reports.After testing a few apps, one should clearly stand out.