Match songs are at 256kb, which will consume ~120MB/hour of listening.
Yes, you can download music beforehand, and play it while on the road - ensuring that you don't use data by turning off the 'use cellular' option. The entire library will still be displayed, but songs not downloaded will be greyed out and not accessible. Music that is played via Match but not downloaded is stored in a cache, and for some period of time not re-downloaded, so if you largely listen to the same music, you should only have to 'stream' it once.
Match does not play well with syncing directly from a computer - you can do that, but when you next turn on Match, it will remove the music that you have synced.