Don't know if I will hit all the areas in one posting but here goes...if you oscars are fairly small and you watch your water chemistry closely, you should have no problems cycling your tank with them, oscars are fairly tough fish....don't put just any rock in there though, you should do some testing on 'wildcaught rocks' before adding them in. by all means, boil them, i even soak them in bleach and then back in freshwater...then take a measurement of your tap water after it has sat out for 24 hours, then immerse your questionable rocks in the water for a few days, then remeasure all of your parameters....lots of rocks will contain minerals and such that will leech out into your water...you should feel safe if all parameters are unchanged from your original reading, any swings in levels indicate something is leeching...sounds like this is your first adventure in fishkeeping and if it is, i would suggest staying away from oscars at first--they are tough fish, but they have quite a few special care requirements...if you are dead set on them first off though, do much, much reading before buying your babies, because those 2 inches cuties can be 10 inch monsters in the first year, and although not especially aggressive, they will eat anyone in the tank that they can get a hold on, and as they grow bigger they do become somewhat more aggressive--individual personalities will vary, and oscars are very intelligent fish, so there is a rather wide variation...and as far as each needing 50 gallons---chances are they will demand it quite soon, especially if you are unlucky enough to get 2 males to start off, and you will be buying another tank rather soon--you may find that 50 gallons is too small, as these fish do attain a massive size for aquarium pets and they are quite powerful--they will overturn decorations, uproot fake and real plants, dig gravel out from under rocks and turn them over--which if they aren't carefully placed in adequately strong tank, burst your tank bottom...they are famous for attacking and destroying tank heaters, ramming glass hoods, sometimes until they break them, etc..they are easily bored and must find entertainment, and unfortunately their intelligence doesn't help them in self preservation aspects when they begin their little tirades...i have heard mine hit the top of the tank from UPSTAIRS!! and they aren't even full grown yet! they can become territorial if kept in smaller aquaria, and refuse to allow any tankmate to survive, and they are picky about which oscars they will live with too...just because you have a male and a female, does not mean that one will like the other and they will live happily ever after...they are south american cichlids and like relatively soft, acidic water, although they are somewhat tolerant of water conditions, this could be a problem with adding untested rocks...they are high, high level waste producers, require frequent tank cleanings to remove all the food they shred that gets wasted out of their gills, which is a lot! sometimes it doesn't look like they are actually eating anything! they do eat a lot, more than i would have imagined before ever keeping them myself....you will need a LOT of filtration, and LOTS of room for biological media to grow, you must be very careful not to disturb the bacterial colonies, especially after they get bigger, because of the enormous amounts of wastes that must be broken down to prevent their water fouling, and as for the air bubbles! they aren't necessary, but my oscars love to sit over the bubble disks!--you will definately need some powerful powerheads to agitate the water to increase oxygen available for both your oscars and your bacterial colonies....phew! all in all, if you want to keep oscars successfully you need to do much research and experiment with your water chemistry monitoring and maintaining your bacterial filtration without any hitches first--i would suggest starting off with something a little less involved to learn the ropes with, but if you are gonna try it now, you definately need to buy some books on fishkeeping, fish stress, water chemistry, cichlid aggression--primarily south american, because africans motives usually are a lot different from southies, water test kits, powerheads, powerful filters--not necessarily canister, there are some sufficient power filters out there, but you need to know what you need before you go--powerheads, python gravel cleaning kit or some substitute, basic fish meds in case you screw up, water conditioner, a big bottle cuz you are gonna need it!, etc....and you should be reminded that nitrate levels will escalate rather easily in such a tank, and if uncared for, will inhibit your buddies growth significantly and diminish his overall well being....also read up on hole in the head disease, it's rather prominent with new fishkeepers when keeping oscars--they need a wide variety in their diet for happiest fish, but you have to be careful with live foods and the introduction of disease, etc....and contrary to what some may say, your oscars can get along quite well without eating any feeder fish--mine eat worms, veggies, pellets, meats, etc. with absolutely no difficulty--you will soon find they will eat just about anything that falls into the tank...
and one last thing--you don't need to provide lots of hiding places unless you are planning on a bigger tank with other kinds of fish, oscars don't care much for hiding! lol, just the opposite--they wanna be SEEN!
8) 
