Regarding #3, it's probably just easiest with the way the product is set up to request the render in new window true/false at deploy time for an FI. The variable in the extension hints to the installer whether to set a database flag as true or not on installation, as you pointed out. But we have the ability to flip that database flag at any time. So while it's listed in the extension for convenience as a way for the dev to message to the one installing the extension later (who might also be you in a sandbox stack, for instance), they can be controlled separately.

The VENDOR_CONFIGS are a great way to have things stored in the database passed to the extension at runtime, but it's a bit of a chicken and egg usecase here. Can't seed the database with things from the database. If you just list this in extra data or whatever that field is called on your deployment ticket, we'll make sure to get it set up correctly when installed.