I generally use the same sight, US MK9. I don't think it's necessary but it can't hurt. All you need is a dot and a circle. Some good shots just use a dot. I like a dot and 2 circles. As Bustr has explained in detail elsewhere, the circles can be used for setting the proper lead. You need to be aware of your angle off tail, the angle of your flight path relative to your target's flight path, in order to use the rings accurately.
When people say they shoot by feel it means they learned the correct sight picture from experience. Because there are so many variables in shooting a moving target with a moving gun it's best to educate yourself with theory and gunnery practice so that you can also eventually shoot by feel. The training arena and the lead computing training aid, the green crosses you put your sight on, are your quickest education in proper sight picture.
Some WW2 aircraft did have lead computing gun sights but we don't have that in AH.
Part of good shooting is setting up the shot and waiting for a good shot before firing. Also, with wing mounted guns try to shoot at your convergence distance.
It's hard to learn ACM from a book but it's a good place to get clear on the theory. ACM simply consists of turning, slowing down, and accelerating, with regard to the bandit's position and lack of interest in following your game plan. You need to understand turn performance, turn circles, and pursuit curves. Your target may understand them too so then it's a contest to maximize performance. You learn basic ACM best when flying against the same performing aircraft. Once you know the fundamentals you can use them against aircraft with different performance. A trainer or training partner can help you put into practice what you're reading. Film with trails turned on is a great tool for understanding turn circles, pursuit curves, and the effect of speed on turn performance.