I've heard that if the wheels are rusty around the spoke holes and the polishing process thins those area further it can make them unuseable as the spokes could pull thru. I t depends how rusty the rim is I reckon.

Hi, to be honest polishing is very simple. You remove material using different grades of abrasives until you get a smooth surface. I am uste you will have heard of the different grades of abrasive papers eg wet and dry where 1000 grit is fairly fine and say 60 grit is pretty coarse. The grit size refers to the number of grits per a specific distance. To be honest I don't know the strict definition but is doesn't really matter. With wet and dry the 'grits' are stuck to a paper where as with a polish they are suspended in a solution in the case of 'brasso' or in the case of a buffing polish the grits are suspended in a 'soap' which is transfered to a buffing wheel where the friction generates heat which melts the 'soap' making the polish into a viscous liquid.
The bottom line is that to polish a piece of metal that has seen some action over the years you have to smoothly remove metal til younreach the bottom of all the scratches. you might start with afilea and then work your way down through the various grits of abrasive papers and then though the various grades of polish. You use different types of buffing mop for the different grades of polish. Usually for rough stuff you will start with a coarse polish ( often brown ) using a sisal mop (like cut string) then move onto a sewn cloth mop
with a medium polish and finally use an open linen mop with a fine grade polish.
The problem with polishing critical stuff like wheel rims is that to get a good finish you have to remove metal to the depth of the deepest rust pits, obviously making the material thinner than The manufacturer intended. Polishing is hugely expensive because it is very time consuming. Wheel rims especially, it is often cheaper to buy 'pattern' replacement rims, but many restorers don't want to don't want to do this as it spoils the originality of the bike.
Ralph