As said before if you want to build a gaming PC to play GTA V straight up, you will be paying alot more then £300, if you do chose to go with the PC that you have just chosen you will not be able to get the full potential that the PC version of GTA V has in which it will really not be worth as you have a PS4, I myself primary bought GTA V due to the 60fps and the beautiful 1080p settings the game brings, my opnion, wait a little longer till you have a higher budget and go all out, or, do what I did, buy bit by bit it will be much worth it in the long run.
My opnion I cannot tell you not to, nor to go ahead with it.