[One (M7) Q&A, Help & Troubleshooting] bye4now12:
Hello World! First time poster, hoping to get some help :) Based on the forum rules I decided it was safer to post here, please let me know if this should be it's own thread and I'll remove the post. Questions are highlighted in BLUE Italics to make things easier.

Two weeks ago I finally bought my first Android device, an AT&T HTC One from Craigslist. The seller told me it was rooted with KitKat 4.4 (via ARHD 40.3) installed, which I knew was the latest version of Android and meant it had been "modified", but I underestimated the implications.

After activating the phone at AT&T with a new sim I found two big problems:

I can't sign in to Google Accounts. Google Play and Google+ in Sense both say "There was a problem communicating with Google Servers. Please try again later." I've tried using my two existing Google accounts, as well as creating new ones or even made up accounts and always get the same error. I was able to add my Gmail account to the built-in Mail app.

The GPS doesn't work: it can't determine my current location via built-in Weather app or through Google Maps in the browser

I've spent hours and hours over the past two weeks scouring the forums and think there is something wrong with the ROM that was installed. I believe my best approach is to either flash with a new ROM or revert to stock and start from scratch. Rooting was always something I intended on doing, but I'm the kind of person that likes to have full control / knowledge of the end-to-end process and get nervous coming in without any background information on exactly what was done.

This is my first non-iPhone smartphone, and while I was an Informatics major and comfortable around computers, I'm terrified of bricking my phone. I'm appealing to these boards to help confirm my assumptions and thoughts to make sure I don't end up with an expensive paperweight. I've included what I believe to be relevant information based on my research.

Bootloader Screen:

The following is general information taken from the About Menu:

Software Information

Android version: 4.4

HTC Sense version: 5.5

Software number: Android Revolution HD 40.3 by mike1986

HTC SDK API level

Next screen after clicking "More"

Kernel version:

3.4.10-g31f7883;

root@abm007 #1;

SMP PREEMPT

Baseband version: 4A.14.3250.13_10.33.1150.01L

Build number: 4.06.1540.2 CL283265 release-keys

Browser version: WebKit/534.30

Would I be better off flashing with a new ROM or reverting everything to square one then re-starting from scratch? There seem to be a number of tutorials on the latter, though they've also all been heavily cautioned that it could brick the device. My concerns stem from the fact that if the GPS and Google Play stores aren't working, are there others areas that may have been corrupted?

Assuming I flash with a new ROM: I was planning to follow the process outlined HERE:

1. Do I still need to go through the Unlock, Recovery and Root steps?

2. If I were to re-do those steps (even if redundant) could I potentially harm my device?

3. Is there anything special I need to consider going from ARHD 40.3 to 51.0? Or do I simply "flash the ROM"? Can I wipe the device during this?

Please let me know if there is any additional information that would be helpful. I apologize for the novel, I always try to be as clear and thorough as possible. Thank you in advance for your help, I sincerely appreciate it. Really looking forward to getting this squared away and fully enjoying my beautiful new device!