Rudy, let me shoot from the hip with some advice. Take it how you want but I am not having a go at you.
1. Make sure you have thought out carefully what you want.
You seem to have different ideads with every post. 29SW, then agressives (pirannahs I think), then 55 with Cichlids 1st Oscars, then Mbunas, then Dempsies, then back to oscars. Then your tank grows to 90
gal. I am sure that all those ideas are great and would be so much fun. When you change tackt all the time it makes it SEEM like up change your mind and it is hard to give you the advice you want.
2. Accept advice.
No-one said they hate you. Sometimes people would like to guide you accept that guidance and grow from it.
3. You don't always have to have the answer to everything.
A lot of people who have been in your situation are giving worldly advice that most teenagers miss out on. You keep coming up with far fetched ideas about your future. Right now enjoy being young, things won't work out a smoothly as you hope but you will face those hurdels when you get to them. All you have to do now is think of your options, not decide what to do.
4. No-one is criticising you.
You are in a forum where adults speak their mind. If you disagree that is great, but be respectful please.
5. We all want you to have the best aquarium set up that you can.
We will give you advice about how to go about it. That is what we do and we also want it to siut your lifestyle, budget and future. Any tank bigger that 55 gals is a LONG term prospect. We want your fish and you to have no problems in the long term.
I have said enough, but I wish you all the best with what ever you decide.
P.S. Please post some pics of your Blue Gourami and Koi please I love both Gourami's and Angels.