Ok, so the deal about launch scripts is:
They are placed by the dbp system in a directory as configured in /etc/dbp/sbp_config.ini
They are not capable of overriding conf or anything like that. If a package wishes to export an executable that is already present in exec_dir, then dbpd will detect the collision, yell about it in /var/log_dbp_messages and refuse to export that exec for that package. If a collision occurs, the package that was identified the latest will probably end up launching the program/game of the package that was scanned first, or not launch at all. When packages are removed, the exported launchers are checked for a signature first to avoid removing anything that the DBP system didn't place there.
As things are configured right now during development, exported executables are placed in /usr/local/games, which has low priority in PATH and is not visible by root. For a more production environment, I personally suggest a new location dedicated to the DBP system that comes after core system utilities, and preferably after installed programs.
The reason for not having them local is for better integration with environments not using the traditional graphical style. A prime example is tiling WM:ers that use dmenu_run for launching stuff. This shortcoming of the PND system is one of few things that annoyed me enough to even get started working on dbp. Typing dbp-run <package id> <path to run script> in dmenu-run is an unacceptable solution.
On the matter of avoiding collisions, I suggest a helpful predictable name (say, name of the game) and if a collision is plausable (also available in debian repo, etc) then suffix with package name or something. There will be machanisms added later to specify packages that cause collisions, both dbp:s and deb:s.
EDIT: And, regarding screenshots:
This could be solved at repo-level. Removing or adding screenshots to the package is not a terribly complicated thing to do on the repo, so getting it right at first is not critical. On package level, it'll only be implemented as a couple screenshots inside a directory in the meta-zip. If they're there, they're there.