Tiny home power question

Hello, We recently acquired a tiny home with the intention of renting it out. Its right next to our on the grid house and my question is this: It came with a preinstalled 50A/30A 240/120v (split circuit?) box with a 4 wire cable (looks same as 240 dryer cord) coming out of that that was cut by the sellers to move the home. To get power to the tiny, its my understanding that I need to likely connect that cut 4 wire cable up a sub-circuit breaker box (w. 50a breaker) branched from the main house breaker box. But we also have a 50A hot tub sub-circuit box nearby w/ two spare slots (which currently have 20A & 30A breakers in them) for adding more circuits, which would be much easier routing than from the main. Is there any reason I couldn't put a 50a breaker in one of the spare hot tub breaker box slots to achieve the same thing as setting up a whole new breaker box?

Thanks in advance for any guidance on this.

 

But max general purpose 120 volt receptacles and lights can be no more than 20 amps or 15a if wired
with #14. Does the tiny house have a breaker box? It will need one.