Okay, it loads with the codes now, but the character selection screen is still the same (none of the characters added by the pack are there) and my stage selection screen is really messed up and is filled with Pokemon Stadium and Hanenbow over and over again.

I'm still having this problem.

If I understand what you're doing correctly, you only took the GCT from Nebulon's pack? Are you using the CSSRoster.dat?

Yes, I only took the GCT from Nebulon's pack, and yes, I'm using the CSSRoster.dat.
This is the path of the CSSRoster.dat:

U:\private\wii\app\RSBE\pf\BrawlEx

There's also a CSSRosterx.dat in the same folder.

Okay, it loads with the codes now, but the character selection screen is still the same (none of the characters added by the pack are there) and my stage selection screen is really messed up and is filled with Pokemon Stadium and Hanenbow over and over again.

Okay, so I loaded it with Gecko with the hook type set to AXNextFrame, but the character roster is the same. Is the gct that comes with Nebulon's pack missing a CSS expansion code? EDIT: I think the problem is because before the game loads, Gecko says something like "Error: Too many codes 623 Lines Found 424 Allowed"

To use brawlex with riivo you need the proper xml. Might as well use gecko my friend.

Where us the Riivo XML then or what edits do I make to my XML to make it work? I don't want to use Gecko, which doesn't work for me anymore. I just get a black screen and Gecko never loads.

I'm probably being stupid, but I copied the files from Nebulon's BrawlEx pack, with the RSBE01.gct that came with it to my SD card and made sure Riivolution's Ocarina Handler was set to AXNextFrame, but I get a black screen when I try to launch Brawl. I assumed the BrawlEx pack had all the needed files, but I guess I was wrong. What do I do after copying the BrawlEx pack to my SD card? I haven't modded Brawl (or even used my Wii) for a long time, so maybe I'm doing something wrong in Riivolution, too.

I normally have both of of them every time I use a hack, but I was thinking, to save space in my SD Card, can I have just the .pac/.pcs files?

I'm trying to do a Toon Link over Peach/Marth, but it keeps freezing the game. Please help.

How do I get a .rel file of characters, and how do I use them?

There's a lot of reasons this could happen. First, let's define "I changed everything to Toon Link's data."

You didn't just rename the TLink's files and put them in Peach's folder right? That won't ever work.

No. I opened her files up in Brawlbox and replaced them with TLink's files.

I made a Toon Link over Peach hack, and it freezes when I try to go into a brawl. I changed everything to Toon Link's data except her FitPeachEnrty00, 01, 02, 03, etc. What did I do wrong? 

This will be a great guide for me. But no offense, telling people to downgrade their Wii is the worst advice ever. Here's what WiiBrew says about downgrading:
"WiiBrew recommends that you run the latest version of the HackMii Installer and then optionally update your Wii to 4.3 using Nintendo's official updater.

Only update using the official update procedure. Downgrading or installing patched updates is unsupported, dangerous, and may permanently brick your Wii." Also, 4.2 and 4.3, as far as I've seen, don't affect brawl hacking at all. The only thing is that you must use the newest version of Riivolution because older versions were blocked.