Basically do you understand anything about Psa at all? If not look up a tutorial in the help section or look for WackaAlpaca's tutorial on Youtube. After you learn a bit about Psa work you can then understand what they're talking about.
Well for starters you can't use sfx with Gecko. You need Riivolution for that. Since you're already using Gecko, download BeyondYou's Riivolution hack that can be found here in the vault. Most of your folders will stay the same, however a few will change and that will be included in the instructions. You will need to download a common5.pac. You will find your logo in common5.pac->sc_selcharacter. Sfx will go in your Sounds folder in a file called smashbros_sound.brsar which you will also have to download. You will need to download the program Sawndz from here in the Tools section of the vault to inject your sfx into the smashbros_sound.brsar. After you do most of this I, or someone else can give you further instruction.
Are you using the Stage Roster Expansion 2.0? If so then you'll need to add in the Disable Custom Stages code to your .gct or .xml (for Riivo) respectively. If this doesn't fix it, then there could be other issues, but we'll try this first!
Haha, yeah if that's edited wrong it can really screw things up. Make sure you have the latest version of Sawndz which can be found in the Vault, otherwise you can run into some problems.
Yes it does, tho I cannot remember it's limit. Try reducing the quality/file size of your pics maybe? Or possibly use a virgin common5.pac and see if it loads.