Here is a small and seldom-discussed consideration: If you use 10 gauge wire, that has about 1 ohms per 100 ft. Not much, right?
If you figure 10 amps on average for 2 wires only, for 250 ft (allowing a round trip plus some extra wire for connections), the wire consumes 25 watts. At 24 hours per day that comes to 219.15 watt-hours per year. At 10 cents per WH, that is about $21.92 per year warming up the ground.
With #6 wire, you would divide that power loss by 4.
If you were drawing 10 amps through 1 leg of the 240 only, that same math would hold, because 2 wires are carrying 10 amps each. If you had 10 resistive amps through both hots exactly, the neutral would carry no current. If there is a mismatch, that could factor in, but for estimating you could disregard. You could do the calculation using only the current of the highest-current hot.
Now you probably will not average 10 amps. To the extent that your loads are only occasional, the less this would matter.
Hey, you said you were here to learn. ;-)