I have five. I use these rules to create my own universe.
1. One character, one figure. Current exceptions are Alternators Ravage and ROTF leader class Optimus Prime. Alternators Ravage is my all time favorite, so I won't let him go. ROTF Prime is just too awesome to go for now.
2. No repaints only if no choice for non-customizable characters. Exceptions are Classics seekers, Sunstreaker/Sideswipe/Red Alert, Tracks/Wheeljack, etc.
3. For aftermarket figures that cost too much, find other lines to replace it. I'm mentioning Classics Ratchet and Cliffjumper here. They are replaced by PRiD Ratchet and Prime FE Cliffjumper.
4. For figures outside neo G1 lines out of customization, buy them or keep them if they fit in the characters I want. Like ROTF Bludgeon and Animated Arcee.
5. Scale matters.
Yep! That's right. So still no FOC Blaster because he is too big. Also no matter how cool MP Soundwave is, he is too big.
These rules so far go pretty well and my figures count is still lower than 80. Well, I count combiners as one.
Oh! I should add one more. For the characters I totally don't care, don't buy them.