Every one of your questions are the ones that are dangerous to answer.
I can tell you a few things.
My 32 S&W bullets are all either 68 grain lead or 71 grain FMJ so any bullet in that weight range should suit you well.
Small pistol primers are the only option. The brand is up to you, however you should pay attention to a good reloading manual for the correct primer/powder blend.
You really need to refer to a loading manual like the Lyman, Speer, or Hornady. All of them are focused on their own bullets. However, you should within reason be able to work up a light load with most lead bullets in the weights and shapes they recommend. Read them to find the correct powder for the velocity your looking for. Cowboy loads are generally on the lighter end of the loading spectrum so you have much less recoil but can still send the bullet downrange.
I don't cowboy shoot but have friends that do and they have their own recipe and most of them shoot 45's, so they won't be much help either.
I know I'm probably not telling you something you already may know, but the question is an open one with way too many variabbles to give you a sold answer.
You might get lucky and have somebody here that shoots cowboy competition and can give you a working recipe.
I wouldn't shoot FMJs in an old lemonsqueezer. I'd use any of the various 75-78gr. lead RNs offered by the commercial casters - nothing heavier than that. Use whatever brand of brass you can find. Starline doesn't list it anymore, so you'll have to get it wherever you can find it.
Wonder who still makes loading dies - and do they keep them in stock? Huntington Die Specialties will sell you some dedicated .32 S&W RCBS brand dies.
A charge of ~2.0gr. of either W-231 or Unique behind that bullet will approx. duplicate factory ballistics. There are slightly better low-pressure choices of gunpowder (like PB or SR-7625), but I don't know what you have available. The ammo factories continued to load .32 S&W ammo with FFFG black powder well into the 20th century. That's probably what your revolver fired when it was new and is probably the "safest" - though dirtiest - choice. A case of "real" FFFG black powder filled to the base of the bullet would be the proper charge. Do not under-load a BP charge....and JMO, but I do not recommend any of the BP substitutes for your revolver. They are either highly corrosive or subject to unexplained pressure spikes. Some have been proven to be unstable over time.
Speaking of pressures....I love to shoot old guns...but I'm scared to death of most of the late 19th Century American-made top-break revolvers I see - even S&Ws. Soft steel alloy and a weak hinge joint are an iffy mix, IMO. Hope yours is OK to shoot.
Thanks for all the information. I will do a lot of research before putting my loads together.
I found that Lee has the dies available and Magtech has the brass. This is a good start. I wish that there was more information available for these old guns.