Hi! This is Kelda writing. 

I'm really sorry for the late reply. I was away from Korea, and their internet connection was bad. 

So I'm now answering just right after I get back to Korea. Sorry for that!!

1. P.E 와 I.E 가 같은 말은 아니지만 같은 의미란 뜻입니다 

electron 이 eject 되기 위해서 promoted to the highest energy level (of which n = infinity), then electron will have a higher P.E by that much gap. 

Potential energy is dependant for each gap between electronic shells. 

2. The gaps between shells are all different. It doesn't have to be same for each gap. Actually, there is some formula for that calculation (which is called Rydberg equation), but it is removed from AP exam criteria. 

그저 energy shell가 나누어진 데로만 energy가 정해졌다는 것이죠?  --> So what you wrote is correct, their gaps are different, but determined for each element. And shells are not continuous, they are all separated. Their gaps will be affected by the number of protons and the number of electrons and their interaction (attraction and repulsion as well). 

3. You should clearly know that ionization energy has a different tendency to the atomic radius. But it's not enough. You should be able to explain it in terms of effective nuclear charges or shielidng effect or Coulombic forces. It will come up in the FRQ section. 

I hope it helps!

Thank you!