--- I already have lots of designs for in-system defense, so the new spoilers don't have me worried too much. I tend to use big, slow ships that are well armed and well defended for attack and fast, short range ships with plenty of firepower for defense purposes. STOs for important worlds, with them being handed down as new stuff is developed, etc.
--- I favor Corvettes of 3,125 tons and Frigates of 6,250 tons for such duties, with the Corvettes operating in one system from a local in-system base and the Frigates operating across a few systems from a regional base maybe one or at most two jumps from their assigned systems. All systems, regardless of size, will have one or more fighter bases if it has anything worth defending in it. Bigger or more important systems might have dedicated Escort Frigates, while empty systems might get an Escort Base for moving supplies through.