Some questions

When a unit aquires an item, can the units' weapon model be removed and be replaced by the items weapon model and not just overlapping the old weapon?

I need to make some sorta trigger that can make you hold ONLY ONE of a particular group of items like swords and shields and stuff like that.

somehow i feel like learning jass but it seems too complicated, the tutorials aren't too easy to understand (lol).

I can help you with the last one. Download JassCraft (found on this web page somewhere; use search) and just screw around a but with it. It has all the natives on the right with a handy search so you can locate what you need. You can also view various JASS tutorials found on this web page (don't forget to check the submitted tuts as I believe there is a pretty in-depth one there.

For number 1, you have to either edit the skin, by making the weapon transparent, or by editing the the model by removing the weapon. The first method is the easiest IMO because it doesn't require any special programs.

For question 2, you have to come up with a way to classify the items (some people use levels, others use the built in classifications) and then loop through the slots of the triggering unit. If you find a duplicate item, drop the manipulating item.

And how do i do so?

You make an Alpha Channel to hide it.

Whats an Alpha Channel? Btw : Im a little new to this so..

No need for alpha channels. Get Wc3 Viewer and extract and convert your skin to .tga (select 32 bit). Now open the tga in a program that opens .tga (Like photoshop or Gimp) With 32 bit, it allows for transparency, so erase the weapon so it's transparent (may require you to copy the layer to a new layer to remove the background heading). Now save and convert it back to .blp with WC3 viewer. Import it to the same path it was in the .mpq and viola, no weapon.