font design - The logic of kerning classes

I am a beginner with FontForge and I would like to know:

Whit is the best logic to create classes. I mean: I have to kern, say, VA but Va too. Obviously, I have to kern a lot of other glyphs with a. But the first class I created is composed by all glyphs to kern together with V, and the second one by other glyphs, including a, to kern with other glyphs and with different features. Which is the more efficient logic to create these classes?

1. 
   

   I create a (left) class with F and P, and a pairing (right) class with some other glyphs as a, o and r with a certain kerning. After, I create another (left) class with T, and a paring (right) class with some other glyphs as u, y and again r with different kerning. But FontForge tells me that r is already in use and I must delete it from one of the two classes. So, do I have to delete r from both previous classes and create a new, third class only with r to pair it with both left classes in different ways?

   
   


2. 
   

   Same for some glyphs followed by comma? It's evident that n. generally is okay without kerning, while r., w. or y. need different spacing. The same for a hyphen between o-o and n-n: If the spacing is the same, it looks okay between the two o, but not between the two n. Which is the most economical way to handle these situations?

   
   
   


3. 
   

   For apostrophe in my font has generally a too large space on the right, which is the way to apply the kerning to all glyphs that follow the apostroph itself? Is there a wildcard like * in Bash?