Brake release

surface rust on the brake band will wear off if its only light. just make sure its nice and free and the drum turns nicely. the clutch you might have to dismantle becuase its several pieces sandwiched together. and the corrosion could be inbetween the plates see if with some penertrating oil you can get the mechanism moving and turn the input shaft on its own(trans in neutral) if you can do that no need to dismantle it just yet. but if you do dismantle it you can change the throwout bearing if needed and clean everything and inspect for wear.
the problem with the whole hog approach is its gets expensive, it a lot of work, you can create a rod for your own back it needs to be tempered with that fact of these are retired and antique machines there not going out earning paid work. what you would do with a true working machine you wouldnt do with these as its overkill

My memory is not keeping up, might be easier if everything about your tractor was in one post. As I don't remember if you have had it running and driving, or just towing it around.

If the master clutch releases your good for now, unless you have buckets of money to rebuild to new. I would get a bit of lubrication on all pins, linkages and sliding collars. But just a little as you don't want it on the clutch it self. One of the most problematic parts are steering clutches on all makes and models if they sit a lot. Keeping them under roof does not always do any good. I have one that was barn kept in a very dry low humidity area and they still rust/stuck together. The one side worked to drive it a mile to load and haul it home. But after fixing the non working one, I wanted to see just how it ran, and in a few hours the other clutch quit working as well.

So once you have it running, and driving, you can evaluate what else needs work. Unless you want the full restoration.

Oh since your question is about brakes. The only rust problem I have had was brake band rusting to the brake drum. I was surprised trying to tow it did not break it loose. Getting it exposed as you have yours pictured, it was easy to free it. Then I could again roll it with a very small wheel tractor in the flat yard.