Your on the right track by coming to the forum here, best move I did. Lots of extremely helpful people with solid advice. I came here in March as a complete noob, and now I am just a semi-educated noob.

I spent many hours backtesting and hope that it was helpful in my initial investment in LC. Be very careful setting up your automated stuff as I set up automated on another site and it was set up incorrectly. So I still sit on a bunch of notes I do not want and have had defaults from them.
I no longer invest in LC primary and have moved solely into the FOLIO market. I know that FOLIO can be intimidating to learn, but there are good deals to be had there. It is definitely not for everyone.
Follow the forums here and dig through them more. But for the most part, you have to decide what is the best course of action with the amount of risk you want to tolerate.
Personally I would not worry too much about LC underwriting. Ya I know that some defaults are up a bit on some of their lower classes of notes. I only use FOLIO now not because I do not have faith in LC, I do it because others do not have faith and want out.
I think you are on the right track with your filters, might even want to snug them up even more. When I was buying notes I had I believe 9 filters. 60k min income, no notes from CA, NV, FA or AZ, own or have a mortgage, under 20% DTI and FICO over 680. These were just me and sure others would disagree with some of them. But the more you filter the less notes means bigger cash drag.
Good luck!!!