300# or a bit more is about right for a drum, and a few small holes at or very near the bottom works good, just be ready that the drainage leaves a black stain on concrete garage floors
, but it washes away.
To summerize my Mag stoker, I took the pusher assembly all the way out, wiped oil over all the parts and the inside of the hopper, and sealed the small stuff (with the oily rag) in a giant ziploc on the basemet shelf. The stove gets a light scraping/sweeping all around the inside, then gets "painted" down with a syrup-thick paste I made out of flour and water, which just dries and sticks.
The thing I try to remember is 1- get as much ash out as possible, and 2- seal the metal. I've also heard of oiling the stove, and I read here that some guys use a small light bulb to keep the inside warm and dry. I just like the flour paste because it's what the first owner used (he gave me the idea) and it works for me.
Hope this helps, good luck!