That is totally an individualistic number. I have run six AAS compounds at a time with three to four ancillary drugs, but I've been at it for awhile now. In all honesty though, you can still make great progress with just testosterone at a decent dose.
Multiple compounds are often utilized for the unique aspect each brings. Tren for nutrient partitioning and ridiculous anabolism, nandrolone for joint benefits, masteron for androgenic benefits, so on so forth.
The key is taking things slow and adding one at a time; there's no need to dump grams of AAS into the body all at once as it's not only likely a waste, but side effects can run rampant - and become difficult to solve.
Hope that makes sense.