I've flashed this phone so many times I don't even have to look at instructions anymore. I've also lost count. LOL.
Biggest thing with flashing is making sure you've got a good CWM (Clockworkmod). I still use 126.96.36.199 from my Icarus days. It hasn't failed me, If it's not broken why fix it?
Another thing is that you have to make sure when you put the rom on your SD card, It is in the main section and the file is unzipped. You also want to make sure the size of the actual rom matches the one on your SD card.
I do Gapps and MetrOFF together after I've already booted into a new rom. I also use Titanium back up for all my apps. With my Contacts though I've had trouble with Google keeping track of them so I keep a copy of them here on my computer just in case.
Also, If in doubt do a FULL WIPE. It will not hurt as I've done it each and every time. Though some people would think I'm being overly cautious, I have not had a failed flash yet. :] Good Luck.
P.S We all started out somewhere. Mine was with Icarus, Which I believed to be a great first time rom as it teaches you how to put CWM on a phone and also how to format the SD card and do an SD-Ext. Then it teaches you how to flash a rom of course! ^^.