RE expert drums - they are one size for all quantities of film used. unlike other 25XX and 15XX tanks where you can adjust the chemical level depending on how many films you have loaded, in an expert drum you must use the same amount every time. when using 2523 tank with 2509 reel, it is enough to use 100ml of chemicals if you are only loading 2 plates and 270ml if you are loading all 6. not much to save in 3000 drums anyway - they are very efficient.
RE the chems: once you mix the developer you have at least 6 weeks to use it all up. i have not used felxicolor in a while, but if it is how i remember it, it lasts after mixed, in a well stopped bottle for many weeks.
the bleach will last indefinitely pretty much, if in well stopped bottles, but you will start noticing white flakes of crystallization after a while. this does not affect the bleach and does not affect the films. once the bleach is used, if you intend to use it again, it will go bad a bit quicker, 2-3 weeks. but bleach and fixer are easy, you can always rebleach your films if you need to clear them out.
fixer will last the same as BW fixer, long long time. final rinse might oxidize, but will also last a super long time, this is the easiest thing to overcome, you can use ANY wetting agent such as kodak fotoflo agfa agapon, ilford ilfotol, tetnal mirasol, and the best i have used - sprint stabilizer - none of these have formaldehyde, which makes them better for you and the rest of the world, and if you buy any small container of the above list it will last your entire life time, if not some generations succeeding you.
hopes this answers your questions!