I am trying to design a pie, but I'm not sure what to take into consideration
We can't answer #1, because it is simply a matter of opinion.  You need to consider two things: crust and filling.  Since you already have a good pie crust, this is just about filling.  Flavor aside (as that is personal preference), you are going to want to consider consistency, that is, how the filling will behave when you cut the pie.  You are probably going to need to experiment a bit.  Traditional thickeners are flour, tapioca, and corn starch. Other considerations include visual appeal and flavor, but again, that is a matter of opinion.