Gou Lou Cai,
I am going by the ‘36 keyword formula’ as shown in LKWs seven star vol 1 book.
Please bear in mind that different teachers have different interpretations. So I am sharing my opinion only.
I understand most of the principles to a basic level but I am interested/confused about these particular ones.
Yes, sometimes it might be counter productive to read different line’s interpretations.
1. Ou (Hook)
Gou (ou) is a middle level (face/throat/chest) and relatively long distant intercepting move. Usually making contact with the wrist area of an incoming arm. The energy can be diao (ward off/casting aside), Zhan Nian (contact and adhere) and Chan (wrapping and reeling). It’s more than meets the eyes.
2. Tiao (intercept)
Diao (tiao) is again middle level. It’s intercept and ward off and casting aside usually casting the incoming forearm away and behind you from a high line to a low line. In some ways, it’s almost like a slip in boxing term except that you have the hook hand preceeding; hence, Diao Jin (advancing).
3. Chan (contact)
Zhan (chan) is to make contact. It doesn’t have to be a hook. It can be any part of the forearm upto the tip of the elbow (back of hand included). Usually Zhan would be use in conjunction with Nian (adhere) in order to listen your opponent through his bridge. Zhan can be delivered with a Gou (hook), but a Gou doesn’t necessarily has to be Zhan.
These 3 principles seem to be pretty much the same? What are the differences between each? Here is what I have concluded so far, so please correct me if I am way off.
This is typically the idea of Bian Hua (variations and changes). Tanglang is holistic and organic in nature. When it’s broken down into cellular level, the powress of it will be diminished as well. That’s why these keywords should be drilled and emperically studied.
Starting with Chan. This is the idea of contacting the incomming attack, so in theory Chan is represented in both Ou and Tiao.
please see above.
Ou is usually combined with the skills of Lou (grapple) and Tsai (pluck). Ou catches, Lou secures, and tsai plucks the opponent downwards towards the attack.
Gou is mostly applied to the wrist area. Lou (grab) is working on the elbow and upper arm grid. Cai (pluck) can be used in conjunction with Gou and Lou. But it can also work as a single handed grab or snatch against an incoming arm (mid to high level). It requires very good hand eye coordination though.
Tiao seems almost the same as Ou. What is the difference. In the above example, Ou simply catches the attack and then it is the grappling hand that pulls down the opponent.
However, in my head, Tiao does both the catching and the pulling, therefore it can be used exclusively without needing to be combined with other principles.
Diao in Greater Meihwa Line is more of a grab/catch and pull to the side. You effectively change your opponent’s line of attack. Gou is more of an interception and follow up with the other hand (Lou). His and your relative position and distance don’t change much. Remember Tanglang (the insect) in nature uses both claws in conjunction. But we human can choose freely depending on the situation. That’s where the art is, my friend. 
Am I way off?!?!?
Give me your insight
I think you are quite close IMHO. May be working with drill such as Zhan Nain and Feng Shou will help you see more. Just some thoughts to share.
Warm regards
Mantis108