John
On your AR absolutely leave your light on even for patrolling. You need to exercise good light discipline, but there are plenty of situations when having one is worth while. Also keep your AR us unchanged as possible, be a familiar as possible with the controls so you are not changing what you are doing. Lights are not that heavy, so shedding weight for patrolling should not be an issue. If you are patrolling and come upon a situation where you would want it, putting it on then is not realistic. Chances are if its not mounted, you are not going to carry it along.
I am a big fan of lights on my handgun. On all of my "duty" guns I have Surefire X300Us. they have the primary benefit of illumination and also carry the secondary benefit of adding a little bit of heft to a polymer framed handgun. The difference in a Safariland holster with light and without is fairly incremental. I prefer the Surefire, but also like the Streamlight TLR-1HL. It is a very durable, bright light that is a bit less expensive than the Surefire.
As far a sights I dont beleive in "night" sights. If it s light enough to identify a target then they are fairly useless. If it is dark enough to have them be effective you are shooting at a shape and not identifying your target....not good. I like Dawson precision sights....Black black rear with Fiber Optic front. It takes very little light for the fiber to "glow". You will need the raised model for either over a Can or for use with an RDS if you decided to go that way.
RDSs are an interesting item. I have tried them and have gotten away from them.....but will probably give it another go. I found that shooting an RDS is different than any other pistol you will own and I fount it difficult to transition well from RDS to non RDS pistols. First it is different than picking up the front sight. You need to wait until the dot comes into your field of view, some even say that that find themselves moving their head around to try to pick up the dot initially. This can make getting off a good first shot slower. Once you have the dot however follow up shots and transitions can be much faster. The big problem I had was the difference in aiming a RDS. With sights you have a clear front sight with "blurry" rear sight and target. With an RDS you focus on the target and leave everything else blurry. This is the same as shooting a dot on a rifle which is nice, but if you will be going back and forth between pistols it is something that will take getting used to. Here is a good link to an picture Breach Bang Clear did.
https://www.facebook.com/BreachBangClear/photos/a.257032267727287.54105.257009451062902/1209966372433867/?type=3I have tons a friends that love them and others like myself that are on the fence with them. I dont know of anybody that cant stand them. The problem is the cost to get a good quality RDS to try. Low cost RDSs are not worth it because of the beating they take on a handgun.
Avoid Lasers like the plague. I have seen more people shoot like crap destroying their fundamentals because of pistol laser.
Obviously these are just my opinions.
Chris