Every system you try will have flaws, or you may salivate over a feature that appears in other software.Some familiar names are mentioned frequently: Stessa, Apartments.com, RentRedi, TenantCloud, Innago, RentManager, Avail, Rentec Direct, Doorloop, etc.I recommend conducting thorough research on each app online to understand their offerings, pricing, etc.

I understand cash offers give you an advantage in any market - but is there any specific reason it's more difficult buying out of state without being a cash buyer?

Private institutional lenders actually offer 30-year fixed loans underwritten to the income of the property.

I want to offer her $350,000 for the condo (its a fair price for it), 5% down payment ($17,500) and pay her monthly $2,000 for 3 years, after which I would refinance and pay her out.

IF the property is different - then maybe the program  being offered is the only one thats  avaiable 

If you already manage your 4 properties, you can build on those systems you already have in place and offer your services to other landlords and investors.

Generally the listing realtor won't show your offer favourably with a vtb.I personally found the best owner financing comes from motivated vendors, in the private market. 

I ran across this company/tool here on BP last week and have been looking over what they offer. https://www.houseflippingspreadsheet.com/Yes.

I worked for Zillow Offers.

I’m not offering legal advice so do your diligence.