Advice on Swap to Dot 5 - New MC

Anything will work with almost anything, but you might have to re-engineer the front to rear proportioning.

For instance, your 10x2.5 rear set-up is way to powerful for the front. If you run no proportioning at all on a set-up like that, then when you brake hard, the rear of the vehicle will unload weight onto the front, and the rear brakes will lock up. This is a bad situation. If the car is not driving in an absolutely straight line, the rear end will skid around and try to pass the front. If this happens at speed, and you don't be ready for it, then you will be facing backwards likitty-split.
Most vehicles are engineered for about 85% front brake/15% rear. On A-bodies this would be 10x2.5 on the front and 10x2s on the back, but the 10x2 rear shoes are closer to 1.75; and there may be a proportioning valve in the line.
So as yours stands you will need an adjustable P-valve in the rear line to limit it's effectivness.........
Unless you are also running big and little tires. With big boots on the rear you can increase the rear effectiveness, on account of it's harder to skid those big tires compared to the smaller fronts.
As to the M/C and drum brakes;
The M/C has to have enough capacity to move all the shoes out to all the drums, and to be able to compensate for the occasional non-working self-adjuster. The tendency with drums is to forget about the adjusting business. So the pedal goes lower and lower and one day the rears don't rub anymore. Since they don't do much anyway, you probably never notice. But eventually you will run outta pedal and the stopping is pitiful. So you gotta keep that in mind with your engineering and also to keep aware of the pedal travel.

As to Dot 5, It needs to go into a pristine new system. If it is polluted with non-Dot5 then it's effectiveness will be reduced. And you cannot pump out every drop of the old stuff, by pumping in the new behind it. So if retro-fitting, you have to flush out the old. As for the stuff itself; it's a great product. Mines been in there since year 1999, and seems to work same as it ever did. One thing I did notice tho is that it likes to weep at the M/C lid. Mine has a bailing wire on it and I just can't seem to make it tight enough. No complaints.
I'm a streeter tho with a manual trans, so I hardly even use the brakes.Except I do run bigNlittles 235/60-14s up front,295/50-15s out back. And KH 4-pistons up front with 10x2s out back..... and no brake proportioning. ..IIRC the rear WCs are 15/16... but may be 7/8s, I forget; 1999 is a long time ago.
I wouldn't hesitate to use Dot5 again.
For a drum/drum dual system, both reservoirs could be the same size. Or the reservoir to the front brakes could be bigger....... like the one you linked. On a factory Mopar the rearmost reservoir goes to the front brakes.