First what kind of owner will you be the one that culls when illness or disease arises in turn breeding a very healthy sustainable flock or one who will treat to a degree, or one who will go all out i.e.: feeding tubes or surgery or using a sling and treating for possible weeks.
All are good ways to go and none are wrong but the type of person you are will require different tools in your kit.
#1 would be just Amprol and a hatchet
#2 would consist of vitamins, Amprol/corrid, blue kote, bacitracin, etc...
#3 would have various meds for various circumstances, large needless syringe, tubing, slings, hospital quarters/pens/bins, disposable scalpels, vaccines etc...
if I had more time I would be more complete but I am sure others will chime in
