Luis. There is no such thing as a perfect model. No matter how experienced you are, you will always feel you can do better. Then, even seasoned builders have bad days (believe me!).
Never feel ashamed to post your work. If you truly want to improve, post your pics in the forum and just make it clear you want people to give you advice as you want to improve. That way you will get real meaningful feedback. This community is all about helping each other, whether it is for build advice, painting or research. There are plenty of posts in here where guys have benefitted from the advice. This is an example of how someone posted their model, got feedback and improved the result. Kudos to Maclee for doing so:
As to weighting a model, lots to consider. I believe that weight should be depicted without adding any material if you can avoid it. As manufactured, most kits show weight distribution where the vehicle would be basically horizontal. If you want to depict a tank climbing or crossing a trench, then the change in weight distribution on tracks/wheels/suspension will change ride, height etc. If you want to show that, then you are best adjusting the height yourself, raising or lowering torsion bar arms, etc.
Here is an example on one of my unfinished builds. The Sherman Crab flail mechanism was heavy and it shifted the weight forward considerably which meant even on a level surface the suspension on the real thing was not the same as a standard gun tank. To depict that, I had to do surgery to lower the ride height of the forward 2 bogie units. The first was dropped to almost maximum (see the arms are almost horizontal), then the middle part way and the rear were left normal. So when viewed from the side, it is a noticeable forward dip.
I also added some lead weight to the rear as the resin conversion is heavy and I did not want it tipping forward, but on a normal styrene kit, that would probably not be an issue.
Then, some modern kits have ‘movable’ suspension. These are not designed to be glued in situ and if you build them like that, then adding extra weight will eventually torque the suspension and the kit will sag lower over time unless you glue the suspension solid.
Hope this helps