We've kind of been changing/creating the rules as we go, so I understand your confusion. How it works is: we sign up, claiming at least our starter Pokemon. As soon as you catch another one, you post in this thread stating which species. The post may contain as much or as little information about it as you'd like, but you have to at least tell us what species of Pokemon it is. Before the 4th badge, we may only have up to 3 Pokemon (just to speed things up). After the 4th badge, we can choose to catch up to three more Pokemon for our party, bringing us up to a maximum of 6. The same rule about posting applies here; you have to at least tell us the species of Pokemon, but any other little surprises (a couple perfect IVs, egg moves, HA, etc) can be left out. Should one of your Pokemon evolve after you claim it, and before you get the chance to battle anyone, you don't need to update or post again - count it as another little "surprise". Evolutions can be easily predicted anyway so long as you know what level Pokemon we're dealing with (and we will).
If you want to swap Pokemon, you have the chance to do so at the beginning of each "section". So, for example, tomorrow when we start the Knuckle Badge section, everyone will get a chance to swap one or all of their Pokemon. Keeps things fresh, and this wasn't meant to be super competitive anyway. Just for fun :)
I'm gonna re-write the rules in a bit though and add everything we've tweaked/come up with together. I'll also add you to the list of players right now, and your FC to my system :) Welcome to the play-through.