Issues activating SGS3 SPH-L710 on Sprint with Custom ROM + lots of problems

Hello all!

This is my first foray into the world of custom Android systems, and I'm having a hell of a time with it... if somebody would be able to help me out, I would greatly appreciate it.

First off, the situation:
I am on Sprint, and I recently bought a Samsung Galaxy S3 (SPH-L710) from Sprint to use as a backup phone, I used it for a while on Stock, then deactivated it so I could give it to my wife. First though, I wanted to put a custom ROM on it, and experiment/play around a bit and see what this world of options could do for me. Long story short, I ended up flashing an AICP ROM, and everything seemed to go smoothly, but when I went to activate the phone on my account again and it would not work no matter what I tried (details below). I figured maybe I could activate on the stock setup then just restore my custom setup, so I tried to revert to my stock ROM backup and I couldn't do anything because I was constantly getting messages that various programs had closed... Then I tried to wipe and restore my custom ROM backup and I get stuck in a boot loop... so I tried to flash a stock recovery and I get stuck in a boot loop... I'm out of ideas here, and now I'm stuck with a phone I can't use or do anything with, and I can't activate.

Details:
The initial rooting/install process seemed to work ok, and was fairly straightforward. I followed various guides on http://galaxys3root.com/ to get my phone rooted and backed up (Don't recall which ones now, but I've read through so much by now I don't know if it matters...).

My phone:
Samsung Galaxy S3 (Sprint) SPH-L710
Modem: L710SPRDNJ2

My Desktop:
Debian Linux

Here's the steps I performed:

1. Rebooted phone in Odin mode


2. Downloaded CWM S3 Sprint Recovery from the http://galaxys3root.com/ website (can't find the link any more)


3. Flashed the CWM recovery using Heimdall then rebooted phone into CWM


4. Installed SuperSU through CWM, then rebooted


5. Checked that the phone was rooted successfully (it was), then ran Titanium Backup on the whole device to my SD card, then copied the backup files to my desktop computer


6. Rebooted into CWM, and performed a backup through CWM, then rebooted and copied the CWM backup to my desktop.


7. Downloaded AICP Rom for my phone from here: http://downloadandroidrom.com/file/G...E-20150707.zip, put it on my SD card, then installed it through CWM and rebooted


8. At this point, I was happy with how everything was working, so I did some minor theme customizations then made another backup through CWM, and copied it to my computer, but I did NOT run Titanium this time...

After all of this, I tried to go ahead and activate it through the Sprint web service. This process failed continuously with an unhelpful error message of "Sorry, this device can't be activated right now". I then got on Chat to see if they could activate it manually, and then the problems began. They did their thing activating the phone, but when I booted up I got no data connectivity, and couldn't make calls, and the SIM was not changing over to the new number. I was on the chat with them for over an hour trying to get the situation resolved, but that finally ended when they started asking me to punch in ## codes, because I discovered that none of them worked on my custom ROM. Some quick research told me that this was non-trivial to get around so I had them switch everything back and I started researching the issue.

I found this thread: http://forum.xda-developers.com/show...light=sph-l710 that looked like it would let me do what I needed from the custom ROM, but I couldn't tell if it would fix my problem for sure, so I figured "I'll just restore my stock setup from that backup I took, activate it and update, then start over". This is when things got really frustrating...

1. First I rebooted into CWM, went to 'backup/restore', and restored my stock backup


2. Rebooted, and as soon as I got past the lock screen, I get inundated with messages of various apps being closed unexpectedly.


3. I researched a bit, discovered the issue may be caused by stale dalvik cache, so I rebooted into CWM, cleared the dalvik cache, formatted the /cache partition, then tried to restore the stock backup again, but this time I get stuck in a boot loop.


4. I then rebooted into CWM, tried to restore the backup of my AICP ROM, only to be stuck in a boot loop as well.


5. Trying to get into any usable system, I rebooted to CWM, cleared dalvik cache, then formatted /cache, /data, and /system just to be sure, and re-flashed the base AICP ROM I started with. This worked fine, and before long I had stock AICP back


6. Since I still couldn't get the phone to activate in the custom ROM, and my backups are apparently completely useless, I rebooted into CWM, wiped dalvik, /cache, /data, and /system again and tried to install a different stock ROM I found in the XDA forums (here: http://forum.xda-developers.com/gala...4-4-2-t3010642) only to be greeted by another bootloop

At this point I've spent well over 24 man-hours trying to get this to work, reading, researching, flashing, etc all to no avail. Nothing I do seems to work, and it seems like every article, tutorial, or forum thread I read either has nothing to do with my device, is too old, or doesn't describe my problem.

I'm at wits end, and am so frustrated I'm ready to just give up and smash this device and buy a new one... My questions to the community are as follows:

1. I know I screwed up on a couple of things, but in my initial research of doing this there was no indication that these were even things I needed to watch out for... Is there any more organized sources of information for doing this sort of thing?


2. Does anybody else out there use Sprint on a custom ROM, and if so how you you pull this off


3. Where else have I screwed up, and how can I fix this situation? (My end goal is still to get the S3 onto Sprint with a custom ROM)


4. What can I do differently next time? I would like to figure this out and do it to other phones and devices I have, but if it's this much trouble every time, I just don't have the time to mess with it.

Thank you in advance, and I appreciate any information that the community can provide.