You will receive a prompt to update but will lose root if you accept. If that OTA happens to eliminate a root-hole then you are stuck without root until another method is found (if one is found). It's best just to wait for some devs to incorporate an OTA into a ROM.
Rooting is easy as there are one click options available. ROMS are a completely different beast. And arguably the most fun part. But before you even think of flashing, CREATE A NAND BACKUP. This is an unscrewed with image of your OS that you can flash in case you make a mistake. Do this with one of the Recovery programs available for download.
Then you just download ROMs. Follow the instructions to the letter, and read them through completely first, and youll have no issues, all fun.
*Cyanogen is a ROM developer who names his ROMs cyanogen. He usually only makes ports of his ROM for HTC devices, with some exceptions.