Does bicycle rim thickness come in different sizes what is the core size of the rims and what is the best material for bicycle rims in weight and strength?

Where to start...

First off, there are plenty of different wheel sizes out there, so the overall diameter of the rims will vary accordingly.

Most rims are of aluminium alloy extrusions, basically an U-shaped rail that's rolled into a hoop and joined up. This means you can have the same extrusion used in several different wheel sizes just by rolling it up a bit tighter or looser.

Most aluminiul rims have about 1.5 mm wall thickness.

Rims can be either double, or single-walled. A single-wall looks just like a shallow U. A double-wall will look a bit like an A.

Double-walled are available in different profile heights. The higher the profile, the lesser the air drag, the bigger exposure to side winds, and the heavier the rim becomes.

There is no "best" material. They all have different characteristics, so what's "best" is determined by which features you prefer the most.

Carbon fiber rims are probably the lightest, and can be really strong too. Trouble is the failure mode.

Metal rims tends to buckle and dent if you hit something like a pothole, while a CF rim is likely to just shatter, which is a lot more dangerous. Some CF rims have also been known to overheat and warp during long descents.