The number of discrete gpu's you can have is a function of the motherboard; the cpu has nothing to do with it.
If friend is talking about the number of compute elements in the integrated graphics included with the cpu, that is another question.
Generally, the latest generation of processors will have mote capable graphics capability which is partially because of more included graphics processing elements.
If you will use a discrete graphics card for gaming the integrated capability is irrelevant.
As to performance, there is a distinction between multithreaded capability and single thread capability.
Multithread applies to apps that can use all the cores/threads you have.
For such apps, generally, I5 is stronger than i3, and i7 is stronger than i5.
OTOH, if your application is single threaded, as many games are, the issue is not so clear.
Most games can effectively use only 2-3 threads so I7 is not particularly helpful.
Moreover, the single thread performance of a i3 may well exceed the single thread performance of i5 or i7.
For example, the passmark rating of a I3-6320 is 6073 total, and 2245 single threaded.
A I5-6400 is 6547 total but 1826 single threaded.
A I7-6700 is 9959/2138.