Bringing power to a shed

When I was building my shed a neighbour asked if I was building my "dog-house" - I replied we had no dog, but 2 cats, and my wifr would KILL me if I built a cathouse - - - .

Other than not being legal (you can't run multiple circuits to a building) I suppose it works but you would have been better off running 4 strands of THHN/THWN or 12/3 UF and using a 2 pole breaker. If you really think you are going big out there run #8 on a 40a breaker and put in a 2/4 slot disco box out there. That also requires a rod. That would give you two 20a and a 20a 240v or four 20a 120s for not a whole lot more money.

There's also another circuit or 2 for remotely-controlled Christmas lights. That's what I have.

If that wire was 100 feet long, you are talking about an extra 30 watts or so. That is pretty perceptive on a nominal 1440w heater

Used to live in the SF Bay Area. Common practice was to drop a redwood 2x4 on top of the UF cable. No way you are going to accidently harm the wiring. I think PG&E used to require that on buried entrance wiring.