In a nutshell-and from experience-you can drop about 1" without anthing being a problem. Over that and you begin to enter the serious upgrade zone. If you want to drop a 5th gen more than 1.5" be prepared to scrape driveways and speed bumps. You should also consider that stock shocks were not designed to last or even work properly with a large drop.
I've written this before-for EVERY 1" of drop there will be ~0.75 degrees of negative Camber. That means that at 1.5" or more you probably will need camber kits to get the suspension back to what Honda specifies. I assure you that the ONLY way to know this for certain is to get the car aligned after you do the lowering-you need to anyway to reset the toe-in.
As to brand of coilover-you do get what you pay for. I prefer either Skunk2 or Ground Control with Koni shocks for my race car. If that is not a solid option then consider using Neuspeed Sport (H&R too) springs for a very nice drop and comfy ride. The Neuspeed Sport springs give my 99 SS a very good stance and they work well with the Koni "yellow" shocks both on the open road and for track days (HPDE).
Good luck and happy holidays