My actual system folder contains 
50 extensions plus a few extras for my scanner and printer and 
19 control panels.
This system folder is used in 
ALL my G4 macs (from iMac TFT to MDDs) without a glitch for years. It is based on Mac Os 9.2.2 but contains parts from other system versions up to Mac Os 8.6.
With this system folder I have worked on Photo Editing (Photoshop), Graphic Edition ( Canvas, Illustrator, Pagemaker/Indesign), Video Editing (Premiere and Videoshop) ,Text Edition (MacWrite), Spreadsheet (Excel) and Codewarrior and a few games (Star Wars Racer, Medal of Honor, GLTron...).
It runs Cubase, Logic, Live, and Pro tools. And a selected collection of VST plugins.  For Performer 3 needs an extra extension.
It has all the main functionality, Open Transport, Quick Time, Open GL, Apple Scrip, Java Runtime, etc
It runs the 95% of the software that can run on Mac Os 9.
Of course I haven't ever needed to use extension Manager.
With this system folder the Macs is 
fast, uses 
less RAM, and it is 
easy to find and repair any trouble.
The "minimal install" folder was based on my system folder. I had to  remove the preferences folder and a few items more to let enought space to DieHard for adding the remaining CD content.
In fact I havent removed the startup screen, even later I have made this one:  


To reflect the fact that this System folder is mainly intended for startup in a CD ROM.