I took a look at your file, and something that directly helped already was to adjust the naming convention by removing the dot (.) in the object-names like a.1, a.2 etc,
and also I re-did the Smoothing Groups from UV shells. Overall there were not many issues, mostly a few hard edges because of the UV shells & highpoly model.
All the objects from "a" are also attached together when I was working on this model, after this first testbake I noticed some issues because the objects with "a" in the name were seperated.
The UV shells were in some cases seperate where it would be better to keep them as 1 shell, such as those 3 things on the top (image below is the result after tweaking some stuff):
In addition, I re-arranged your unwrap to use the space more efficiently, my personal approach (for my own unwraps) is that every pixel counts, while of course maintain enough padding between the shells.
I noticed a few big uv shells were not visible in the model itself, not sure if these could be visible later on but as the model is right now I'd leave them out of the model (and out of the unwrap as well^^).
Here is my approach for the unwrap, with on the right side those invisible elements selected: (Note: This unwrap is made quite tight, with the mindset that it's gonna be a 4k texture. If you use a smaller texture later on I'd recommend having a bit more space between the shells )
Now for the highpoly part, I'd like to recommend to make use of softer edges. Of course, the real world has some sharp edges on objects, but in 3D models like this with normal maps it's better to make every corner a bit softer (if possible) so that the normal map looks fantastic with nice transitions. If the highpoly model is sharp; Chances are that the normalmap makes it quite pixelated resulting in harsch edges (or no transition at all).
I have doubled the chamfer amounts (on few areas even a bit more). Also my personal preference is to use only 1 segment in the Chamfer modifier and set the "From Smoothing" option to "Unsmoothed Edges". If you have set up your Smoothing groups correctly, this should work just fine^^ Here is a screenshot of the settings I used on one of your objects:
Still talking about the highpoly model: For tall/wide polygons (big distance between the edges of the shape) it's wise to add some extra edgeloops. You might wonder why;
If you don't do this, the corners of your model will have a sort of "stretched out" look, by adding some extra edgeloops to fill the big blank space they get nice and clean.
Here is one example; The selected edges are those edgeloops which are simply there to support the nice & clean look of the corners
Some final result screencaptures of how it looked after all this was baked down;
I hope this provides you with enough information to solve the problem, I'd suggest to try this all yourself as thats the best way to learn & work with it
Have fun and good luck in advance
Anything related to baking, texturing or sharing useful advice.
Thanks a lot now getting back to it. About the dot, i was just crazy about the problem that i tried separete everything, haha, that's why there was a lot of a(s) and b(s) you know..... And about the UV, i don't have many knowledge yet, tho i'm starting to get used to it. Again, thanks a lot, now i should have all i need to get back and finish my model, many thanks from Brazil :]. Have a lovely weekend.