I understand how important it is to expand your presence in the online marketplace to reach a wider audience.Given the complexity and technical aspects of e-commerce, I would advise you to seriously consider enlisting the help of a professional e-commerce development company.

I would second the recommendation for quickbooks online.

I use buildium, it is on the cheaper side of the online platforms that help you coordinate all stuff within one place from request for maintenance and other stuff like emails to tenants.  

I need a comprehensive solution that can:• Track the property from the initial purchase and closing cost, rehab through ongoing management• Record and categorize all rental expenses• Allow me to scan and store receipts digitally "very important"• Monitor additional costs associated with the properties• Track rental income and proceedsI would appreciate any recommendations or suggestions you might have.Thank you in advance for your help!

Regardless of your level of plain/simple vs rustic vs fancy, you can do it for much less by just going to used furnishing stores (primarily).I used both 1) high-end second hand stores (meaning not primarily Goodwill and Salvation Army), and 2) lower level antiques stores where they have decent pieces for say < $500.

However, if you do want something more robust the most flexible option I've used is "Hemlane" you can check em out online, they are a paid service though, but as I said it is a more robust option than a zillow manager or something similar.

Or is it vast wasteland a pawn shops and liquor stores?

Then just restock every few months instead of doing constant small deliveries.Amazon Locker or UPS StoreSome hosts use an Amazon Locker nearby or a mailbox/UPS store in the area.

I use QuickBooks Online for all of my clients.

Confluence I use for storing and tracking of documents and expenses.