The trickiest part for a beginner is often accessing the plumbing behind the tub, especially if space is tight or an access panel isn't readily available. Ensure you have ample lighting, like the NITECORE flashlight, and be prepared for potentially corroded or seized old components which might require extra patience and leverage from Channellock pliers.

Plumber's putty is crucial for creating a watertight seal between the drain flange and the tub surface, effectively preventing leaks. Apply a generous, continuous bead under the flange before seating it. While silicone sealant can also be used, plumber's putty allows for easier future removal if necessary.

Heavily corroded or seized drain components can indeed extend the project time beyond the estimated 5 hours. Have penetrating oil on hand to help loosen stubborn threads and allow it to sit. You might also need a hacksaw, like the Husky Close Quarters Hacksaw, to cut away old components if they cannot be unscrewed.

While you are not directly working on pressurized water lines that require the main supply to be off, it's a wise safety precaution to do so. This minimizes the risk of accidental water damage if a pipe is inadvertently compromised or if you want to prevent water from inadvertently entering the tub during the process. It also helps manage any residual water in the pipes.