ElGuano is spot on there. Adding 900g to a stock Phantom (plus whatever you will use to mount it) will make flying pointless... it will lift off but you will be murdering the 18 amp ESC's, flight time would be about 1-2mins and landing would be fast and ugly.
If you are looking for a more pro set up you would be wise to look at a Hex copter. F550 is a good choice but maybe better still a Tarot 680 Iron man.
My F450 quad currenty flys for 12-13 mins @ 1.9kg but that is with a Hero3 and a f**k off dirty great 5800mah 4s battery. To get a 900g cam up for more than 5 mins you will need a platform that is happy with a take off weight around the 2 - 2.5kg weight. This won't be cheap to do and I'd say you'd need to take the Phantom budget and double it (When you consider bigger batteries, charges, flight TX/RX, props and good motors).
In regards to other cameras well that really depends what you have in mind for your 'ideal'. I assume you are counting out the Hero3 for a reason? Is it price, quality or function related? (it is a bloody great bit of kit to own IMO... not just for flying).
If you are actually just looking for some fun flying with video then others are using the Contour HD, Garmin Virb, Sony AS30 .... these all have their own traits and most require some real thought on how to mount it (and you can count gimbals out).
Compact cams can work well but, to specifically answer your question, you need to avoid the take off weight going above 1300g (100g above DJI's recomendation).... for this you will need better props (9x5 graupners or Tri Blades) and a 2700mah battery unless you want 5 min flights.
Hope that is of help... keep us posted on your direct needs/thoughts and I'm sure we can help further.
