Where I live we only get some of Coopers international extracts, but none of the brew enhancers or dry malt extracts that I've seen in most of the recipies. Will I get good results if I don't add any of these extras or should I replace them with something else?
From what I've seen/heard, the vast majority of quality comes from your process and the freshness of your ingredients. Get the freshest extracts, hops, and yeast you can start brewing!
Over time you'll learn what you can do to improve your brew with your own limitations. But as long as you can get hops, malt, and yeast (and water), you should be in good shape to make a decent brew.
It's worth noting that if you can't get the specific ingredients listed in recipes you won't really be able to recreate the exact flavor, but you should be able to get reasonably close. Given that you're just starting out though I would focus more on getting a handle on the process and then go from there.
Coopers kits can be brewed without additions. If you just want some reasonable beer then just brew the required style of kit. If you want it a bit more body and taste then brew with one and a half or even two kits in 24L volume. It works quite well. Brew enhancer is a mix of glucose and malt extract so some adjustment to ABV can be made by adding glucose or table sugar.
Are you completely unable to get ingredients through mail order? There are quite a few places that will ship internationally if that's the issue. If its really not possible, then maybe see if the source of your Cooper's kits can order something a bit better. In any case, if that's all you can so, I'd say that fermentation temp should really be your first concentration. A simple swamp cooler setup may do well depending on your climate. If your're somewhere very warm, you may need a dedicated cool area (you want 65F ideally, 68F maximum).
Also, it might be easier for you to get started in all-grain since I would think Argentina has some decent agriculture and Patagonia malts come from your country. You can probably continue to use your current equipment, but just need to add a strainer bag to allow you to do Brew-In-A-Bag... BIAB. There are lots of videos on the internet on how to extract beer this way, and its simple for most extract brewers to do without a lot of extra equipment.
Cheers and good luck!