Excellent practice. I've done extensive training in the area myself. Training in aikido and combat shooting, naturally I wanted to bring the two together. My shooting has informed my aikido, and my aikido has improved my shooting.
First, be sure to wear eye protection when actually using a projectile! The first thing I always do when training with guns, real or other, is to go over the 4 rules of gun safety. (See Below.) I consider it very important to maintain muzzle control while performing a technique. You may not have control of the trigger when doing any technique, so controlling the muzzle is vitally important. Imagine your wife or daughter standing next to you when doing these techniques. The best way to control the muzzle is to make sure it doesn't point at you, points to the ground, points in the air, or points at the attacker.
With these preliminary ideas in place you will find that you can do a number of aikido techniques from a variety of positions and attacks. For those without a gun and beginners I think it is much better to use a tanto and just have uke stick you with it when you move. If you can avoid getting stuck, you can avoid getting shot! If using a gun, (I use a rubber one) be sure to be careful not to break ukes finger with the trigger guard. It is easy to do. Actually, you will find the leverage the gun provides will greatly increase the strength of your technique, so practice with mindfulness just like you would in your dojo.
You have found Kotegaeshi to be an excellent technique. Nikkyos are particularly devastating as well. Both allow you to control the muzzle. Those two along with Sankyo allow for the requirement of muzzle control, so I limit my training with guns to these techniques. Sometimes however you just get an Ikkyo. In these cases I think it is best to go strongly to the ground before attempting a change to the control techniques. The muzzle is out of control for a shorter time, and--let's face it--it's so much easier to change to nikkyo when uke is worried about his hand bouncing on the ground!
If you have done aikido for some time, you will know a variety of techniques to try. If you haven't, just ask your sensei to show you techniques against being held at knifepoint.
One of the things that you learn when studying handgun martial art is the time it takes to pull the trigger. All those people that say you don't have time to do this stuff don't train with handguns! Just like you probably wouldn't go to an aikido seminar taught by a gokyu, don't take advice about gun waza from people who don't study it.
That being said, it takes between one that two seconds minimum to actually make the decision and pull the trigger. Your uke will usually be faster than a real assailant since he knows the game. Someone holding you at gun point doesn't want to shoot you right then (or he would do so), he wants to compel some action or your part. This greatly slows down his ability to shoot. So just train slowly at first, working on mastering the techniques and controlling the muzzle. You will gain proficiency with time and practice. Remember, you can't learn aikido fast! That means both quickly and moving fast. Go slow, get it right. Gun people say, "smooth is fast." It's the same for aikido. Good Luck.
Four Rules of Gun Safety
1. All guns are loaded! Until you have checked yourself. If you put an unloaded gun down, it's now loaded!
2. Don't let your muzzle cover anything that you don't want to destroy. This means you as well.
3. Keep your finger off the trigger until your sites are on the target.
4. Be sure of your target.
Follow these rules and you will not have a gun accident!
For more info on shooting check out the International Defensive Pistol Association (IDPA) at http://www.idpa.com/