The gear you chose is fine.
A heavy black t-shirt makes a fine darkcloth, torso hole fits over an 8x10, stretched a bit the neck hole works well for 4x5. I've used worse real darkcloths and most are also much heavier.
I didn't see mention of tripod and head. Its nice to have a good solid tripod and a heavy duty pan tilt head. The camera will seem ridiculously large. Afterwards even a 4x5 will seem small.
Consider "shooting" for a few hours without film to practice, get a feel for movements, working the shutter, etc.
Remember bellows factor.