There are a lot of enemy spawners on the first stage IIRC, so if you accidentally start destroying them, you'll run out of enemies before you can get a huge chain going. Just stay in the middle if you really want to milk it.
Dashing doesn't increase your combo, but you can kill enemies while dashing into them, so that will add +1. Both dashing and freezing are very important though, and they become more and more important the further you progress. You'll get used to it after a while.