That's about how I felt. I was confuzorzed as hell, too. But I am full researched (lvl 3 100%). I used Golden Goldbulbs and some Speckled Goldsharks later on. I had the GG up to $50 and the Goldsharks to $40. They sold like hotcakes.

Here's the order I went in:
1) Temp/Airater.
2) 2nd Tank
3) Environment Reasearch
4) Sales/Advertising Research

That got some mondo $$ flowing so I could mass produce fishies. Every hour I was making $900. So I started buying the special plants, and then finished research on Environment and then Food.

Now I'm aiming for some big bucks with bigger fish (I hear the Canary Fire-Arrow is a nice one to have). THat way I can start finding new species for my collection .