First time land lord- need advice on rent/income ratio and let fee

[Cindy Joseph]

I have a middle aged guy with a disabled son (wheelchair) who wants to move in our unit. Rent is 1900 and his gross monthly is 4000. He does have 100k in the bank. Would you consider this remnant? I’m in Melbourne FL (1 hour east of Orlando) and the market is slow without much interest. 

He was willing to do a 15 month lease and pay all up front. I think this is a bad idea because taxes?

also they have a service dog and a cat. What is  reasonable cat fee? Should I do a non refundable or refundable cat deposit?