I was wondering if a model could be given both a bow and shield?

Edit: I think yes, because the base profile of a rider of rohan carries a shield and bow..

Yes they can. If you are on foot, you do not gain the +1 defence that the shield would normally give you, but you may still use the shielding rule and may fire your bow as normal.

However, if a model is mounted and it has the Expert Rider special rule, the rider does gain the +1 defence, and so there are no penalties to using either the shield or the bow, except for the fact that mounted models cannot shield. If the rider is dismounted however, he behaves like a normal infantry model, and so loses the +1 defence that his shield initially gave him.

In short, infantry and cavalry models without the expert rider special rule do not gain the +1 defence when carrying both a shield and a bow, but a mounted expert rider does.

Hope this is clear/ helpful

What if I deploy a mordor orc with bow and shield, does he gain the +1 defence in combat?

No.

No infantry model can gain the defence bonus if it has both a bow and a shield. Lurtz, for example, comes with both a bow and a shield and even he does not gain the +1 defence.

Only models with expert rider with access to bow and shields gain the defence (Riders of Rohan, Rivendell Knights, Rivendell Knight Captains Galadhrim Knights) but they still lose it the moment they get dismounted.

Thanks for clarifying!

So If I give Faramir just a shield his defence would go to 6 instead of just 5? And if I give him heavy armour + shield his defence would be 7?

Yes. That's why when we see Faramir he's almost always equipped with heavy armor and shield.