As far as which fish you decide to get I'll tell you a little about my experience. I started out cheap/poor too, about 14 years ago getting 1 red belly. Started learning about other p species through books, and just wanted to try to own every kind I could get. Of course at that point the whole "mr. cheap its only a fish" outlook I had was quickly thrown out the window. Fastforward to now I've owned at least 1 of about 75% of piranha species known, and spent a lot of money. 2 things you should know...1. piranhas are nowhere near as aggressive as the "Hollywood monster" myth and reputation that was given to them. Most of them will bore you. They can however still be dangerous and unpredictable when least expected if your hand is close enough for them to have access. 2. Everyone always asks whats the most aggressive species of piranha. The truth is, it largely depends on the personality and hunger of the fish, not necessarily about which species you get. They all have razor sharp teeth. I have had p's that are very aggressive and ones(species) that everyone says are aggressive but the ones I got were dull. I will say this though. Your chances of getting an aggressive p are very high if you choose a Black Rhombeus or a Gold Mac. I have owned several of both of those species and not one has been dull. Just for the hell of it here are all the species of p's I have owned to date. Red Belly, Caribe, Piraya, Brandti, Gibbus, Sanchezi, Elongatus, BM Elongatus, Gold Macs, Gold Diamond Rhoms, Black Diamond Rhom, Peru Rhoms, Xingu Rhom, Manueli, Medinai.