OS X Random Freeze and updating

First off, thanks for the great forum and efforts here! I am in need of a bit of help...

My specs:

Intel E6850 3.0GHz
Asus P5N-D Mobo (750i nforce I believe?)
150GB WD Raptor 10000RPM
8GB DDR2 RAM
Nvidia Ge-Force 8800GXT

First off, my original issues were freezing during install. These issues were solved by taking out all but 2GB of the ram, and doing a custom install instead of just quickly going through the process. I am now typing this help topic from my fresh install of OS X.

Here's are my current issues:

#1: OS X is periodically freezing. It's random, but always happens at some point or another. It can happen at 5 min, or 1 hour..but it does happen. Any ideas for this?

#2: I installed from Leo4all 3, so my current OS X is 10.5.2. How can I upgrade to 10.5.6 safely?

#3: Are there some kind of kext patches out there that are more reliable stability wise than what was included with Leo4all 3?

Your help is greatly appreciated!

Best Regards,

Cameron