I would find some other strategy(ies) to focus on that give you experience and value in the market. 

Resources including books, forums, podcasts and personal experiences  would be very much appreciated!

House hacking during the pandemic was a smart move, and it's great to see you leveraging your experience to pursue your goals.All the best!

Does anyone have experience with their callers and the training they offer users to help close deals?

Unless you specialize and invest a lot of experience and knowledge into STNLs, I think the risks are just too highly concentrated to dabble in that space.

This would be my first investment and I have no experience, so I know it would be a massive stretch.Any thoughts?

I want to get the experience.

I would only consider this if they can demonstrate they are a professional company with a long history (operating 5+ years would be my standard), and if they are willing to make it financially beneficial to you (higher rent rate, they handle maintenance, etc.).There are a lot of "businesses" that started recently that have no real experience, meaning they've only operated in a strong market.

Does anyone have experience with their callers and the training they offer users to help close deals?

I'm not sure what sort of liquidity concerns that you have, but my experience they are fully liquid.Business bank accounts don't get any interest.