I have so many plugins that even on a smokin’ system, it takes a while for the program to fully load. Can I restrict all but Extension and 3D warehouse from the net?
Extensions are not loaded from the internet, so network latency or bandwidth utilization is unlikely to be the most limiting factor of application startup time. Most extensions do their work only when you actively use them (click a toolbar button etc.). If an extension connects to the internet, then it is most likely when it shows a webdialog (although they usually display offline content) or when it polls a server for usage count or update information.
What you should do to improve startup time is to not load so many extensions from your hard disk by disabling them in Window → Extension Manager.
I was hoping that they were slowed down by referring to the net every time I loaded the program. It’s a shame that I have to compromise convenience for speed.