What advice would you give to a Linux noob? What habits do I need to break? What habits do I need to learn?
Don't panic. I'm not clever enough to run Windows safely, and doubt I'll ever advance beyond XP.
Simplest/fastest GUI, most similar to WinXP is xfce. Try xubuntu to see what it is like.
Get LTS variants.
Try before you buy: get "live CDs" and run them from USB/DVD
Try before you buy: if you've only one computer, create multiple boot partitions wirh windows on one and a linux on another: choose which to run at boot time.
Try before you buy: run VMs with windows as the host and a linux as one of the guests
Try after you buy: run VMs with linux as the host and, say, Win7 as one of the guests.
When installing, create multiple partitions (equivalent to c: d: etc in windows). On one put /home (contains all your files, in /home/tggzzz), on another put the eveything else, leave a third blank and put windows on a fourth.
Use the blank partition if you want to try a different flavour of linux: install that on the blank partition and continue to use all your existing /home files. Choose which one to run at boot time.
While config is often done using GUI utilities, most of that will end as straight text files in /etc (for the system) or /home/tggzzz/.* for your personal settings. You can backup and tweak the text files, unlike the awful Windows registry.