Okay, I'm sorry, but this is not really the best of suggestions. It's a -1 from me. Here's why.
All areas of the server have PVP on
~ @Dausious
No, not all areas of the server should have pvp toggled. There should be designated safe zones. I know you said that town spawns and main spawn would be safe. However, certain areas such as pwarps and chest shops will be compromised. Players will lose part of their business. Plus, the most valuable thing can be someone's head. People may not want to pvp as it runs the risk of them losing their head, making it less valuable. Furthermore, staff need to be exempt or else someone can /modreq and kill the staff when they arrive.
maybe the day before, each player could do /purge yes, or /purge no
~ @Dausious
Why the day before? If someone happens to miss that day, and join on the day of the Purge, they'll be killed. This is not what you want. If we expand the time, it'd be annoying if you forget to do it once. If we make it shorter, someone can abuse it such as doing /purge no in the middle of battle.
Opening someone's doors/trapdoors and such is allowed (so people can't just hide in their homes)
~ @Dausious
This can be easily abused. If we do it so that doors open, people can break into farms or private buildings and set homes inside. Even if someone /purge no, they will still run the risk of players breaking into their house. Also, some animal farms can become open and ruined. This is not what the Towny server needs nor should be allowed.
Teammates cannot harm each other. For each kill they accumulate, they get points. At the end of the 24 hours, the team (or individual) with the most points wins a prize.
~ @Dausious
Uh... This is almost exactly like CTF. You can kill other players for points and at the end of the round, the winning team gets Meebles. If this is what you want, go /warp CTF There is no point in adding something into the server that we already have a similar version of.
Overall, there is no point in adding this plug-in or allowing this. Players can be killed while building, losing gear. The idea of gaining points and not looting chests or risk losing valuables is very similar to the Capture The Flag minigame we have. This plug-in will be open to much abuse from the players and will only hurt the community.