At the least you need some proper screwdrivers, a strap removal tool, a case-back tool, several tweezers, and a place to set the watch so it's safe.
Because I have lots of Seikos, I learned that Seiko makes tools for the bench that are less expensive than the Swiss ones but also perfectly adequare. Here is my bracelet holder (underside holds the tool bits) and a small hand bracelet pin pusher. And the obligatory hammer (needed occasionally).
This tool holds the watch still on the bench and if the watch is flipped over, it's perfect for holding the watch while you are unscrewing its caseback. Better than trying to hold it in the palm of your hand (and safer)
Finally, this one is designed to take off the snap-type casebacks. You carefully screw in the knurled knob, which engages the little pusher against the watch, then press on the top blue tab, which twists and pops open the back.