Welcome to the forum
Most of your questions are answered in detail in the forums.
The stickys above the Gunsmithing forum have a lot of pics and instructions for DIY upgrades. sights, action parts like hammers, sear, disconnector, firing pins, springs, etc x10.
CZ CUstom Shop, Cajun Gun works and more offer a
W I D E assortment of aftermarket upgrades.
Either CZC or CGW Competition rear and F.O. front sights are often used for USPSA and range target shooting. In 98 most 75s have the front sight dovetail that runs from front to rear on the barrel. Retention is by using a small pin the also holds the barrel bushing. If like this, then you are good to go.
The BBL is likely coated with a heat treatment that was black and a little rough looking. CZ did this for a number of years. A number of owners just polish it off with no apparent harm. Others just leave it on.
Several here have threads with pics showing restoration of older and transitional models of the 75. Your pic didn't show up. If you can get the pic posted, it might help identify parts needed.
Sounds like a neat project. Others will chime in with experience restoring the 75s.
Grips: The aluminum grips that accept grip tape are often used by competitors for a firm grip. They come in different thicknesses along with aftermarket variations that meet shooters' needs.
Do some research and be sure to ask any questions you have. Questions are smart.