Hi Firas, with regards to the housing allowance, this all depends on your company, and as Gaby stated, on your position. Accommodation in Abu Dhabi can be extremely expensive, so be sure to factor this in when negotiating your contract. I'd suggest also having a look at our Accommodation in Abu Dhabi page to understand a little bit more about the rental market in Abu Dhabi and the kind of expat housing you can expect in the emirate and the costs involved.
It depends on your industry and how high up on the chain you are. See Employment Packages in Abu Dhabi and also Contract negotiation in Abu Dhabi for more information.