I'm not sure what you mean by 'balancing'. I assume you mean ensuring that both notes have the same tone quality and dynamics, and that you get a smooth transition between them.
Yes, that's 420 pairs of notes to consider, but only very few of them will be difficult. Ignore the easy ones (revisit them later) and concentrate on the difficult ones.

I'm not sure what you mean by 'balancing'. I assume you mean ensuring that both notes have the same tone quality and dynamics, and that you get a smooth transition between them.

Yes, that's 420 pairs of notes to consider, but only very few of them will be difficult. Ignore the easy ones (revisit them later) and concentrate on the difficult ones. Do all the pairs in both directions, up and down.