>What is the Max ram this computer can support ?
To begin with, you can easily answer questions of this kind yourself by going to Apple - Support - Technical Specifications (in this case, click on "Mac desktops" under "Browse Tech Specs by Product" and then repeatedly the "Load more results" button until you reach the older Macintosh computer in question):
Macintosh Performa 575:Technical Specifications
The same method can be used for manuals at Apple - Support - Manuals:
See also sites like lowendmac.com and everymac.com.
>What size should my disk cache be set to ?
>And what size cache should I use? 384k , 764k , etc ?
You may want to look for The Macintosh Bible (for example, ISBN 1-56609-140-3, the 5th Edition, edited by Darcy DiNucci et al.) where detailed information about Memory control panel settings (and many other subjects) can be found.