I am looking for connections to vetted private lending groups to learn more about my options as a smaller lender. 

If you are at the stage, or get to the stage, where it makes sense to split your assets across multiple LLCs there are options other than series LLCs which may meet your needs that are simpler and more cost effective (eg create a second LLC).

I am looking for the best options to get a long term rate around 7%. 

Definitely not bad but another way to look at investment options rather than just COC.  

The house is paid off, and I'm trying to see what my best option is to do with it.I would like to do a full gut renovation on all 3 apartments, but I would like to be able to see if it's possible to convert the cellar to be a legal apartment and get a CO that states "multi-dwelling" instead of "2-family".Does anyone have any experience with this?

We offer all 3 options (4 if you include email which go to a unified inbox). 

Columbus is a great option for appreciation. 

Would setting up an S-Corp be the best option?

Since that is so hard to predict, I think you should move forward if that is the best option for you right now. 

Look at unfurnished, maybe you do better if use that option.