if I put my iTunes library (about 55gb) on to my external hard drive; could I still play the music thru iTunes? And would it sync to my phone ? Of course the hard drive would still be connected to my PC
As long as the drive is mounted to your OS properly, and your iTunes library has it mapped properly it will work correctly.
This is how I have it at home as well. Works fine.
Cheers; have changed the path and now consolidating - once this is finished can I just delete folder from pc? Does this move all in media folder ( even ones that are in the folder but aren't visible in my iTunes library ?)