New Tenants are Pre-paying a Full Year’s Rent. What to do with the Cash?

I’m getting a huge influx of cash! What do I do?

We listed our house for rent a couple days ago. We have fully vetted tenants (two older unmarried adults who want to live locally before moving to Florida/Arizona in a couple years) who’ve offered to pre-pay a full year’s worth of rent after a discrepancy in their income verification. Basically they make money via an annuity and some other non-W2 income. They’re paying via cashier’s check and my realtor and a few other trusted individuals don’t seem to think it’s a red-flag. ANYWAY…

They’re pre-paying ~$46k ($3.5K monthly) for our property
-House worth $500K
-Mortgage ~$400K, $2,350 monthly cost (2.35% APR)

-Our household income is $150K
-No debt other than mortgage
-$20K emergency fund
-$10K additional “in case something goes wrong w/ the house” fund
-$45K saved to buy a car (my CR-V won’t die!)
-$20K buffer in checking account (yes, I know this is a lot, it’s the way we do things)

So, we have ~100K already in cash. Our current plan is to put all the money into a savings account and pay the mortgage with it over the next year, and keep the remainder for a buffer to maintain the house. This would have us with ~150K in cash, which seems absolutely insane to me. I’d love to pre-pay the next year’s mortgage, but I know you can’t do that. So. Can someone suggest what to do with the money in this case? We live far below our means, so I expect to continue to have extra income each month moving forward.