Prep is allowed, but the team will know this (as well as who you've chosen). So will fight accordingly (i.e. the match starts, and the Defenders *know* that Doom has prepped something for them, but they don't know what).
Would Surfer then attempt a blitz, to stop you from enacting those plans? Would Strange hang back, preferring to see what you bring, but raise his strongest shields in preparation? Would Hulk (which I am using Savage here) decide nah, Hulk's the strongest there is, and leap straight at you?
Your prep needs to then account for a blitzing Surfer (for example) whilst Strange *might* be attacking you mystically/astrally whilst Hulk is fisting you greenily etc.
Or it might not. This thread is to test your knowledge of characters and how they fight, but also your creativity.
If you decide to enter the thread with zero prep, then the Defenders also don't fight as if you have prep. So if Zop wants to just punch everyone in the face, can they react in time?