The "magic brush" is a Richeson 9010 watercolor brush. Jerry's Artarama usually has the best price. It is better than a puddle pusher or a glass rod.
Platinum developer is inexhaustable. If you don't contaminate it, it will literally last for years. I had one batch that lasted for about 8 years. Had to top it off every once in a while, but once you "break it in" it lasts for a long time. You can filter the developer through a coffee filter to remove the platinum and palladium metal that accumulates through use.