It makes no difference either way.

>> 2. What is the best way to seal the hole for letting the wires to the crossover out of the rear baffle?

Use a connector plate.

>> 3. Any need to seal the joints beyond the glue? If so, what to use?

As long as the joints are airtight, there is no need to do anything else. It really isn't terribly difficult to make an airtight seal. However, if you're afraid that there is a bad seal in a joint somewhere, I would recommend RTF silicone.

>> 4. Are the Theatre 4 dimensions based on 3/4 or 1" stock?

3/4" panels braced every 18".

>> 5. Back in the days of Bozak and Tannoy, some felt that speaker bases created cavities that could resonate.
>> Would a decorative plinth (base) be bad?

You can make a riser, but don't elevate the speaker too far. It's tall enough as it is. If the midwoofer is elevated more than about 18", you'll create a notch in response from floor bounce.

>> 6. If heavier stock is used, like 1" or 1 1/4", would it still be
>> necessary to re-inforce the cabinet from inside if the drivers are
>> let in to a rabbet?

Even if the panels are thicker, you'll still need bracing inside. Braces preload the panels and provide rigidity that increased thickness just can't provide. As for reduced thickness from dadoing recessed drivers, I suggest using a ring or plate in the driver cutout area. That will give increased thickness where you need it, but not where you don't.

>> 7. I'm so dumb I'm still trying to envision the crossover cable!
>> Is it that the resistors and capacitor are soldered together in a line?

R1, R2 and C1 are built into the tweeter cable assembly and R2 and C5 connect to the woofer with their own cable.

>> Does the order of resistor and capacitor matter?

R1 and C2 are connected in parallel and the pair are in-line with the tweeter. R2 is connected across the crossover output. For the Zobel, R3 and C5 are connected in series, and the ends of the line formed are connected across the woofer. The order is not important.