Service Entrance Wire is only single wire with insulation (they have different colors, but I bought black). It's the kind of wiring you see inside your home's electrical service box. It's got like a clear outer coating protecting the black plastic insulation. You will need to get stranded wiring, rather than the solid wiring just becuase it will be easier to bend and solder to other wires. It's hard to solder 10ga solid wire.
I got 25ft of each 10ga and 14ga, but I think 20ft would be enough for the install. I had plenty of wiring left (4-5 ft).
Just go to Home Depot or Lowe's and they have it all stored on spools to be cut by the clerk. They are priced by the foot.
tk