Removing the rear sight is not hard, but it is best to be prepared before doing it. Make sure you remove the rear sight in the correct direction (the dovetail is directionally tapered!). Removing the sight can be done with a wooden block and a hammer, using a vise with the slide well-protected. But it is best done with a sight pusher, like the MGW sight pusher. A proper sight pusher is less likely to damage the finish on the sight or the pistol.
But as noted, the USB provides a small percentage of the benefits of the kit. So you can leave it alone and see if you like it with just the sear installed. The sear is the main contributor to a lighter trigger press.
Replacing the striker spring can lessen resistance to the trigger press as well, but may/may result in lighter strikes -- too light to ignite the primer (some primers are harder than others. In particular, Russian-made primers are known for being hard, as are primers on some of the top end NATO-spec 9mm ammo).