I am afraid I don't know much about the Highpoint. A good place to look for how to make a rifle CA legal is Calguns.net. Those guys are the experts at building what they want while staying in compliance with California law. In generic terms, a brake isn't going to do very much for a 16" barrel in 9mm. The caliber just doesn't have enough oomph to produce significant recoil in a rifle of that size, and there isn't going to be a ton of gas at the brake to do anything for whatever recoil is present. So a muzzle brake on a 9mm carbine is mostly going to be cosmetic. Doesn't mean there is anything wrong with it, just that it isn't likely to produce a lot of practical effect. As to sights, the older I get, the more I appreciate red dots. There are also some really good options at lower price-points these days. A 9mm carbine is not going to be brutal on a red dot sight, so while you don't want to get something on the bottom tier, you can find something that will work well without spending a lot of cash. You might want to look at the Burris Fast Fire, which is very compact, has good battery life, and an excellent field of view. Good luck, and let us know what you come up with.