Hi,
As others have said........check it out for yourself.
Doha is not as bad as some make out, go for your interview then spend another day or so speaking to people there and looking around. As has been said, there is a big Brazilian community here so maybe through friends of friends you can make contact.
As an FO I cannot comment how much you can save. As 2nd year DEC I am saving around QR20,000 a month. Like anywhere how much you save depends on how much you spend! If you want a 4 bed apartment in West Bay or on the Pearl, have a maid, join the golf club, have membership of the Intercon and own your own boat...........well you won't save much.
For us (2 young children 5 and 8) it was important to get out of company accommodation, find a nice compound near the school. This has the added bonus of not living around your colleagues constantly, not that my colleagues are unpleasant...........but as pilots we like to moan! Your accommodation allowance would be QR12,000 which will limit your choices a little and you would probably have to subsidise by QR2-4000 to find somewhere you will be happy. At the moment rentals are stable, and in some cases have even dropped due to the current oil price issues, but that can change. Working here has, like any job, positives and negatives; speak to people when you are here and get the warts and all version of living here.
If you think you will want to go back to Europe in the next 10 years to start your career again, then I would not come out here in the first place. Go to Europe get your command and once your kids are at Uni you can look at DEC if you want an adventure in the ME!
Good luck