Looking forward to get more familiar with the platform 

Propstream - Data creation + stackingDeal Machine - Driving for DollarsOpen Letter Marketing - Mail ProviderUsing these 3 platforms, you will be able to create lists, research properties, and market to them effectively.

My top priority is having maximum flexibility with what I can invest in within my HSA, second priority is ease of use and convenience of the investing platform, third is minimizing any account, trading, or management fees charged by the HSA provider. 

A great alternative would be simply licensing or leveraging a different web forum platform that already has a mature mobile app available for and that BiggerPockets could simply redirect mobile users to when they open the site.

BiggerPockets is an excellent platform for networking and establishing connections.

You'll lose rent while property is vacant, and you'll probably have to do more repairs to attract a new tenant than you would to keep the current tenant.Is all that worth requiring a tenant to use one specific payment platform?

Some custodians may offer access to platforms with investment opportunities, as well.

Quote from @Isaac Watson: @Charles Perkins are these meetups on platforms like meetup.com?

While time consuming, I did learn a lot and was within $2,000 of my initial budget.

Here's a good folder setup.Bank StatementsCredit Card StatementsProperty Management StatementsMortgage StatementsSTR Platform StatementsInvoicesReceiptsClosing Documents (Purchase/Refi/Sale)LeasesCheck & Deposit ImagesVendor ContractsW-9’s & 1099’s