i have a pentium g right now and i have a little bit of money so thought i could buy it right now and at the begining of the summer i could buy a gtx 770 or 780 so will the i5 bottleneck these cards
Nope the i5 will certainly not bottleneck those cards. Ivybridge is still very strong and a single ivy i5 can handle a 670/680 crossfire setup with no bottleneck so you're good to go!
Hard to say. We don't know how powerful those GPUs will become or how demanding the games of this year will be. Due to the new consoles which has been rumored to launch this year.
We can only ASSUME that it will be fine, which it also probably will be, still take everything you hear in here with a grain of salt.