What a great distro this is!! I used VL up until 6.0 but had audio issues with it, so went back to Mint.... but now with the release of VL7.0, I'm back and lovin' life!!
1- What is the best method to use to make certain the username I defined in setup is ALWAYS the default user at bootup without a Chooser?
Settings --> Login Window -->Security Tab ... " Enable Automatic Login.
2- After I first boot and things settle down, my first use of Thunar takes almost a minute to open up....but after that first start of the app, subsequent starts in the same session are fast! What can I do to make the first start of the Thunar app quicker?
This is normal behaviour for Thunar in xfce4.8.x. At first boot it checks with the Avahi Daemon and does other steps to set up networking.
This is why there is now a Network tab in the side panel of the file manager window.
Instead of shutting the computer down each time, why not try suspending it instead. You won't have to wait for a long boot-up or wait for Thunar either.
3- I tried to install (using VSlapt) PCManFM but it simply won't start. What could I have missed in trying to install it. (I'd like to use it so I can right-click on a file and make it executable, which I can't find a way to do in Thunar.)
PCManFM may be a repository issue I'll look into it.
To make a program executable in thunar, just right click on the file-->Properties-->Permissions(Tab)-->Click the box that says allow this file to run as a program.