If you use Cydia, put it in /var/root/Media/Cydia/AutoInstall/ (you may have to make this directory). Then, reboot and respring. It should install.
You can get Stack here for free, legally. This has been posted several times and is not against forum policy. http://www.steventroughtonsmith.com/stack/contributor.php
Hang loose until the next update. I will include Categories or Stacks support. That way, when you click the "Start" button, it will open a folder instead of a stack.
No, not at all, but will I need to donate to the developer of Stacks v3 as Stacks is going to be implemented?