I can answer four of your questions right off the top of my head:
To do updates, go into Synaptic, enter your root password, and then once Synaptic fully loads, click on "Mark All Upgrades" (don't remember the exact wording on that button -- sorry!), and then click "Apply". PCLOS doesn't have any means to automatically notify you when updates are available, so this is something you'll just have to do periodically whenever you're in Synaptic.
In regards to your last question, as a general rule, it's best to only have one repository enabled at a time, since they could have different versions of the same software as the most recent.
No, there isn't a 64-bit version of PCLOS at the moment, but there is one in the works, and it's my understanding that it should be released in about a month or two from now.
About the 586 versus 686 architecture, I haven't noticed any problems on my computer. Then again, I only have a 32-bit system and no plans to upgrade in the near future.
I'll leave the rest of the questions for others to answer for now.
Merry Christmas and welcome to PCLinuxOS! :-)
Fred in St. Louis