@flamingeyebrows: Yes, the GM Cannon II is allowed. No, the GP01FB and GP02A aren't allowed, as they're not grunt suits.
Only one entry per person is allowed. If you want to build mulitple kits as part of the group build, feel free, but you'll have to choose which one is your entry.
The Geara Zulu you've used in that picture is the Elite Guards type, which is given to Full Frontal's elite guards. I've included a picture below of the Normal Type Geara Zulu. You can use the detailing from the Normal type, as it's a grunt, but the Elite Guards type is probably pushing it a little bit.
If you want to print your own decals, that's fine. Just ensure that they're actual in-fiction decals, and not something you design yourself.