Q1: You should have ADMINISTRATOR level permissions. Have you run a disk utility *Repair Permissions* lately? What OS version are you?
Q2: Yes you should download PPD fonts. No, you shouldn't switch on Text as Black. What fonts couldn't it find? Have you used a font manager? Have you used font doctor to check for corrupt fonts on your system? Have you run Font Finagler (a free download) to reset confused font lists on your Mac? Couldn't hurt. The network is not the issue.
Q3: Change your InDesign doent to speak RGB when printing to the XEROX digital printer. Edit > Transparency Blend Space > RGB will help it send the appropriate color number model to that printer. Also, in the print dialog box, make sure you are printing to the Xerox as the destination color space. (You did install the printer driver fully, right?) The TT fonts should be fine, and generally are not the source of troubles--especially of a color nature.
Q4: Why hasn't the software operator / graphic artist been highly trained in all this incredibly deep software? Is that a difficult thing to do? Oh yes.
Hope this helps,
Mike Witherell in Washington D.C.