If you're just learning to rebuild then starting out with the cheap stuff isn't a problem. You'll want to flame the silica with a blowtorch before you use it to get rid of impurities and manufacturing 'stuff' that might be on it (this cleans it up and also makes it go stiff which helps when coiling)
While you only need 2 cm of wick for the finished coil you'll probably want to start out with 5 or 6 cm of the stuff and about 10cm of wire to make it easier to hold/wrap etc so you'll get 10 coils ish out of 1m of wire and 15ish coils out of 1m of wick.
If you're using twisted silica it has a tendency to fray easily so cutting it a bit longer helps this - and I use the length I cut off as the flavour wick on top so as not to waste too much, you can reduce fraying by getting it damp.