Originally Posted by SimonTS
Start by searching and reading mate - you're far from the first to ask these questions, and there are many threads with the relevant information and guides.
It took me 2 weeks of searching to answer this question. While there are probably other ways, it's difficult with this precise config because most of the root exploits have been closed by OTAs. You can either use HTC Dev to unlock the bootloader or, better, buy a very cheap XTC Clip in the first instance as that will give you permanent hassle-free S-Off.