I would not worry too much about the thickness of not only Gloss Coat but other coatings. It is negligible anyway.
I believe you are wanting to know more about the hardness level. I would not buy too much into the claims of hardness for any coating. They can still be scratched and swirled just as easily as clear coat. They are not impervious to damage. Coatings do help with wash induced marring , which is going to happen compared to a wax or sealant.
When it comes to reapplication this is where I am going to not agree with what was preciously posted. In the time frame of 1-2 years the car is going to need a polishing. I say that because one the longevity/durability is going to vary by the environment the vehicle is exposed to. For example someone who lives in a dry climate will get more longevity/durability compared to someone who lives in a snowy environment where chemicals are used. 1 year actually seems about right for gloss coat anyway.
In that time you will also have some marring. That is going to happen the more one touches the paint. Just the nature of the beast. Good washing technique is important but you will notice areas that will need to be polished out eventually.
Road grime is another thing to consider. Road grime especially in areas that deal with a lot of rain will eventually contaminate the coating and degrade some of the gloss. This is a great write up by Mike Phillips and he makes some valid points.
So to reapply I would go ahead and repolish 1-2 years down the road and reapply. You will remove defects and of course impart gloss with a polishing step.