I don't think you have time and the resources for that. SOFRs are mostly traded by commercials so your counterparties are full time wizzkids.
Pricing and modeling is really complex and you should not expect any "free tools" to do that for you. STIRs in general are a shark pool of professionals and HFT prop - shops so you better prepare yourself before you jump. Online resources, news and information are really rare, so unless you're willing to spend either a couple of grand on education or a couple of months on learning math and coding, I don't think you'll have a fair chance.
They are NOT a safe place to store cash. Look into inflation linked bonds (ILBs)...I'm sure there is an ETF for that