when I get a siding ready, do I just jump wires from the main rail to it for power or run feeders to the main busline?
I would run the wires from the main bus. If it’s a short siding, you might not even need extra feeders, because the power will be carried through from the main tracks via the turnout.
Be careful if you are using “power-routing” turnouts, like some Pecos. Some of these will have problems if you provide power to the frog-side rails and don’t isolate the turnout.
Agreed about it depending. Your turnout types and the positions of their points at any one time will determine if you need to gap the siding and provide separate feeds to those isolated rails. If you get shorts suddenly, suspect the turnouts, and merely leave 1/16" gaps in both rails at both ends of the siding.
Feed from the main bus and isolate both ends of the siding on at least one rail. That way it will be easier to cut in a switch (single pole single throw) that lets you turn off power to the siding. You might want to switch the power to the main too so that your trains have more options when passing each other.
Good Luck,
Karl