OP,
It looks like you have a good start with a VERY heavy duty system!
High Binder is right about the pulleys. You only need to drive one shaft.
The other shaft is just there to support your container.
Look at the red Thumler's Tumbler Model B photo for reference.
One shaft drives the drum from the motor, the other just idles along.
I have a Thumler's Tumbler Model B. It works very well, but is limited to only 2 lbs of brass per load.
Normally, that may be enough, but I have many thousands of saved .223 brass I wish to process and I want a much larger capacity.
The Thumler's Model B is limited by its motor and the thin sheet metal construction
I'm in the process now of putting together a system similar to yours.
I plan to use a 5 gallon plastic bucket with a Gamma seal lid as my drum.
The local bakery sells used (like new) 5 gal buckets for $1.00 each.
I plan to glue and bolt in 3 "baffles" to help agitate the brass and media.
Menards sells Gamma seal lids for $6.97 each. The Gamma lid has 2 parts.
One part has a rubber seal and snaps onto the 5 gallon bucket rim.
The other part screws on and off and also has a rubber seal.
I bought two 1/2 in x 36 in plated metal rods from Menards for $4.27 each.
They are not absolutely perfectly straight, but that shouldn't matter for this purpose.
I also bought two 5/8 in x 36 in metal rods for $8.99 each.
I plan to order my bearings from :
Surplus Center
I plan to use the 2 bolt flange bearing for $7.60 each.
I'm going to weld up a base of 3/16 in metal similar to the Thumler's, but a lot more heavy duty.
I will have predrilled extra holes in the support for the bearing flange on the idler shaft side. That way I can simply remove the idler shaft and one bolt from each bearing flange, flip the idler shaft bearing flange 180 degrees, and accommodate larger or smaller drums as needed.
(note the extra notches in the Thumler's sheet metal support for the same reason)
I already have a salvaged 1/3 hp motor that still runs good and some old pulleys I can use.
When I'm done, I will have more money into the 10 or 15 lbs of SS pin media than I will in the tumbler.
Then I plan to put my Thumler's up for sale