That's about how much my bike was lowered with H-D's Profile shocks in the rear and a Progressive kit in the front - I wanted as fat & low as possible for a daily rider. Plus, the classics that were our inspiration for style appear lower than a modern touring bike.
You'll notice the the lowered rear the most for getting your feet flat and brining down the bike's center of gravity so that might be the best place to start.
The Progressive fork spring kit has spacers for -1" or -2", I'd recommend going with -1" to level out the bike. Any lower in front will put a ding on top of your Classic's front fender the 1st big bump you hit (don't ask how I know).
Also, if you have any plans to change bars, seat or windshield it would be best to wait until after you have some ride time on the lowered bike. Since your riding position will be somewhat different after lowering, the ergonomics of the bike may need some adjustment.