Custom Product Type properties types and validation

Hi there.
Although I have some experience with CMS, I don't have much knowledge with commerce. And I was requested to create a custom Product Type for the project I'm working on.
The problems are:

1. I was not able to create custom validation to some properties (i.e. Property X must be greater then property Y). My custom validation class is ignored, allowing the user to create the product even with the properties values being invalid. The built-in GreaterThanAttribute also didn't sort effect. Also tried to create a custom attribute, again, nothing.
2. One of the custom properties must be a string, but it should have one specific value between some available strings, Like a SelectOne/SelectionFactory on CMS, but these are not available on commerce.
3. The GroupName and Order values from the DIsplayAttribute seems to not be recognized for products(they are ignored), so I can't organize my custom properties.

So, does anyone can shed me some light on these topics? Is it possible to create custom validations to custom products? How can I create a dropdown for that string property? How can I organize my custom properties(on different tabs or even with an Order value)?

I appreciate any help.

Thanks.