(url="http://"http://eshop.macsales.com/MyOWC/Upgrades.cfm?model=34&type;=Acceleration&TI;=%23TimeFormat(Now()%2C+&shoupgrds;=Show+Upgrades")List of Upgrades for Power Mac 8500(/url)
First off, there is no Mac OS 9.5, and if Steve Jobs has his way, there will never be a 9.5. Mac OS X is the wave of the future.
Upgrades to look into:
Memory is a major factor in your upgrade. 96MB is definatly not enough for OS X. Plan on bumping that to 256MB or more before any other upgrades. If you plan on doing anything on Mac OS 9 or later, make a minimum of 128MB.
A G4/450 is possible using the XLR8 Carrier SSE upgrade cards. Although pricy at +$300, it will give you a nice speed boost. Honestly, the bus speed of the 8500 won't run the G4 at full capacity anyway, so your better off buying a G3/400 upgrade instead. The G3/400 upgrade from Sonnet is $150 at OWC
Hard drive capacity is something you mentioned before. Out of a total of 9.5GB, you have roughly 5.6GB left. If you are wanting to really go ahead with upgrades, look into an ATA controller card for one of your PCI slots, and add a 20-40GB hard drive. Combined the two will cost you roughly $200-$250, depending on size hard drive.
Mac OS X is not normally able to be installed on your system, due to it not naturally having a G3. Even with the G3 upgrade, you will not be able to install Mac OS X without some help. (url="http://"http://www.versiontracker.com/moreinfo.fcgi?id=11168&db;=mac")XPostFacto(/url) may be able to let you install it, but if it doesn't, the latest OS you can install is 9.2.2 (9.1 without G3 upgrade)
Good luck in your upgrading.