DPS Question

Too simplistic.

Even if it worked to provide an overall DPS it would be (charge move DPS+ Fast Move DPS)/2. But you do not spend as much time charge attacking as fast attacking so none of it works that way.

It means that your DPS (before accounting for level) is 20 while biting, and 33.13 while crunching. Naturally it's 0 while dodging.
So the overall DPS is somewhere between 20 and 33.13, or possibly lower than 20 if you're dodging a hell of a lot.
But you need to know what portion of the time you spend biting and what portion of the time you spend crunching. You can't determine that in the general case because it depends on energy gain, and energy gain depends on damage received and hence on what you're fighting and the levels of both pokemon and whether you dodged successfully.

Really the DPS of charge moves isn't very useful, since the DPE is (obviously) very important as well.

Way too simple. Here's how the cycle DPS is calculated:

Bite takes 0.5 seconds, does 6 power (base damage), and gains 4 energy. Crunch requires 33 1/3 energy to fire (100 energy/ 3 bars), so 8.33 bites will yield 33 1/3 energy, do 50 base damage, and take 4.167 seconds. Then you fire the charged attack, Crunch, which does 70 damage, and takes 3.2 seconds. So over 7.367 seconds, you do 120 damage, for a base damage rate of 16.29 DPS. Next, factor in STAB, since both attacks are dark, as is T-Tar, multiplying by 1.2 to get 19.55. Then, if you know the defender, you can calculate in type modifiers (super effective, not effective, etc), to get the final CDPS against the opponent, before other calculations.

Those other calculations are based on the ratio of the attacker's attack (base + IV) to the defender's defense (same), so if your level 6 T-Tar attacks my level 30 Blissey, you won't do much damage, but switch the levels and you'll crush me.

The above assumes that you don't dodge at all, and use the charged attack as soon as you can. It also ignores the energy you gain from taking damage, which can change the calculations a bit, putting more weight on making the charged attack more potent against the defender.

DPS is only really useful for determining whether B/C is better than B/SE in general or against a specific type of opponent. In this case, against a neutral opponent, B/C does 19.55 CDPS, while B/SE does 20.27 CDPS, a little better. Against an opponent weak to dark, B/C does 27.37 and B/SE does 25.14, a bigger win for B/C. And so forth, YMMV.