if you have 2 male oscars in the same tank that is anything smaller than a 180 then they can be very aggressive. not saying it will happen all the time but it can and the dominant male can kill the subdominant very quickly. this is really the only time I've ever seen oscar aggression. other than that I wouldn't even say they're particularly territorial...not compared to most other cichlids anyway and when they're not breeding. 
most of the information you need has already been posted. to upgrade as cheaply as possible you'll want to keep an eye on the want ads in your newspaper. you can also check sites like ebay, aquabid and craig's list which occasionally will have tanks for sale cheap in your area. you can also find out if there's any type of fish club in your area. if so there are almost always members selling off unused tanks rather cheaply.
for equipment you'll want to check out www.bigalsonline.com. you can get filters, heaters, python/gravel vacs, water conditioners, foods and about anything else as far as equipment goes for about half the price you'd pay in any store. I have heard that if you print out the price page for what you want to buy that some Petsmarts will price match the bigals online price. that would save you from paying shipping though don't worry if that doesn't work because I've never paid more than $15 for shipping and that was for over $200 worth of stuff including a gallon jug of Prime water conditioner.
oh, and I'd start feeding them small pellets and feed them small portions no more than once a day or even once every other day until you can upgrade and get the water under control. flakes are one of the messiest prepared foods to feed because half of them will get sucked into the filter before the fish have a chance to eat them unless you turn the filters off when you feed. also, the live foods you mentioned you were feeding would be good as occasional treats once they get to a bigger home, but crickets and such are very high protein and the more protein they eat the more they'll poop which of course will foul the water up even faster.
most of the information you need has already been posted. to upgrade as cheaply as possible you'll want to keep an eye on the want ads in your newspaper. you can also check sites like ebay, aquabid and craig's list which occasionally will have tanks for sale cheap in your area. you can also find out if there's any type of fish club in your area. if so there are almost always members selling off unused tanks rather cheaply.
for equipment you'll want to check out www.bigalsonline.com. you can get filters, heaters, python/gravel vacs, water conditioners, foods and about anything else as far as equipment goes for about half the price you'd pay in any store. I have heard that if you print out the price page for what you want to buy that some Petsmarts will price match the bigals online price. that would save you from paying shipping though don't worry if that doesn't work because I've never paid more than $15 for shipping and that was for over $200 worth of stuff including a gallon jug of Prime water conditioner.
oh, and I'd start feeding them small pellets and feed them small portions no more than once a day or even once every other day until you can upgrade and get the water under control. flakes are one of the messiest prepared foods to feed because half of them will get sucked into the filter before the fish have a chance to eat them unless you turn the filters off when you feed. also, the live foods you mentioned you were feeding would be good as occasional treats once they get to a bigger home, but crickets and such are very high protein and the more protein they eat the more they'll poop which of course will foul the water up even faster.