New topsoil would be much better for growth. Soil is not "re-usable" as far as growing plants goes. You can certainly throw the soil in the compost pile and "re-cycle" it though! I would truck in new topsoil if you are planning on some vegetation.
Looks like the overwhelming favorite is to build one. This is definitely good if you want to make something exactly the way you want it, but you have find good bookshelves for cheap if you want something easy. I found one for my son's room for about $80 that looks nice and is fairly strong.
Working hard is easy when you love what you do. I am a competitive person by nature, I don't like to be outdone. So I work hard to be the best. The paycheck helps, of course.
If you don't sand the floor the finish just won't look as good. Sanding is what brings the whole floor down to the same level and cleans off any uneven wear or discoloration. You will end up with a much higher quality floor if you have it sanded first.