I'm using a PC with Win7 64bit, with LR 5.4. I have LRT 2 installed and I'm about to install LRT 3. I spent a fair amount of time looking for a simple set of "installation instructions" but cannot find any for LRT 3. I'm sure they must be here somewhere, could you please point me to them. Should I uninstall LRT 2 first? Should I uninstall exiftool? I've seen mention of LRT 3 Addons, are those installed automatically with the program installation?

Just install the LRT3 installer. No need to uninstall anything. Addons are only for mac.
http://lrtimeapse.com/install