Steel minecarts are
a legal option for embark, but they cost 1500 points. Iron minecarts are cheaper, but you'll still be spending most of your points on one. So, as said, get the ore. It's usually the better option for all metals, especially if you have coal available for purchase.
If you're using power to send carts up to the surface, use the design shown here
. Corner ramps have some odd properties that make them more efficient when used with rollers, making straight ramps much more power-hungry than a tight spiral combined with a section of flat track. Even if straight ramp tiles and corner ramp tiles demanded the same amount of power, a spiral ramp would still be better because of its more efficient power train.
You might also want to set up a macro that designates a 2x2 circle of track to be carved and then moves the cursor either up or down a level. Carving those corners manually is annoying, and if anything is carved wrong you can't troubleshoot it visually. Another good thing to do to increase in-game construction speed is to enable Mechanics and Engraving on as many dwarves as possible. Each dwarf will only be placing a couple of axles or carving a couple of tiles, so the time they take to do the job isn't significant compared to the time they take to walk to it.