Hey, Leonardo.

Well, I tried to download your mod, but this service is forcing me some unnecessary tabs. I hate this. 

Okay, let's see what you need. You want to have a new interface + slots for your pet. I have seen both of these mods and therefore it is possible. But these mods use the same files, so it's not easy.

I think you should take the Diablo mod as a basic, then add slots. You may ask how to add slots? And it's the right question! 
I, and many others, recommend to use reverse engineering. You can learn how to make slots in this mod: Pet Equipment

We can help you, but you have to do most of the work yourself.

OK, now i'm with you. The slots work as intended but the pet stats stay unchanged..
Now my guess is that the pet cant use these stats from items.
I'll dig out the journal menu I've modified to show pet stats - I can remember there were only a few that can be shown.
Next I would check a Stud or Collar Item - affix to see what stats are used and may work with other items too.
The Pet is Playerrelated. I.e. the damage is calculated from your own weapon... I never really understood the calculation behind

thats all I can recommend for now - let me know your progress
cheerio
lolesch