1. I prefer simulating a state to a supranational organization, but considering that our "state" only has two laws on the books, it's not exactly practical to immediately become a unitary state. Current South American laws at the start of the simulation should be considered the status quo until parliament acts otherwise.
Relevant.2. South American countries should be states within a federal state (at least for the time being) treated to similarly to levels of government below regional: it exists, but isn't a direct part of the simulation. Perhaps the GM can occasionally involve local government events (e.g. "Uruguay bans abortion") in the hope that parliament will take action in response.
3. Agree on currency; start out with the status quo, and a common currency can become a topic of debate. Extending the EU comparison, we'll probably need to address freedom of movement between states as well.
4. Status quo until parliament determines otherwise.
5. Same as 4, and perhaps the simulation can start from the mid-2000s as Foucaulf suggested in order to deal with evolving social liberalism, but I'd prefer to start with 2015 legislation.
6. Probably one of the first issues we'll have to address. I'm of the opinion that we should integrate the military to a federal level and establish a federal police force.
7. We absolutely need to standardize citizenship federally.