Our teams idea was that we were going to create an shooter fps. Although before we begin whole rigging animation process we would need to plan the way first person view combined with 3d person (world view) should look like and work together.

Anyway the questions:

1) We want to have both weapon attachment system so for example a rifle with scope and without. And at the same player attachment system so for example armors etc.

So the question is how do we get these 2 to work together. Do we need to have seperate model for every gun for example Rifle-scopeless, rifle-with scope or is it possible to even attach a scope on a weapon model to a bone and then attach the weapon to the hand with everything attached etc?

2) Next we would like to just set the camera in the area of the head and let the model do the animation of shooting etc by attaching different weapons to the model. This way you would only need 1 sets of animations instead of 2/3 sets like in most other shooters like Counterstrike (first person model, 3d person model/animation).

However the question is how would the reload work. Because normally the clip would detach and be thrown on the ground and a new one should spawn in the hand of the model. Is it possible to hide parts of the model seeing as the clip is already part of the model or maybe if its an attachment to the weapon model, it can be deleted and reappear at the bone of lets say left hand ?

first question, yes its possible to attach a scope on the weapon, the very same way items are equipped on characters I would think. Some example is done on armor rendering I think

There is already example code for switching off only the head rendering, different camera modes is the tutorial called.