For SSD OCZ Vertex 4 is much better than Agility. Samsung 830 would be good alternative.
I would, generally, avoid OCZ for PSU. Some aren't too bad, but generally prefer Seasonic, PC Power&Cooling, XFX, Corsair (TX or HX), Rosewill (Hive or Capstone), Antec (Basiq or Gamer).
The H77 mobo is ideal for a single GPU. I presume you don't intend to have 2. If you did, recommend you use ASRock Z77 Extreme 3 for mobo, rather than my original suggestion.
That would be over budget at around £800 but is going to max out anything you toss at it for a while so I would say worth doing some overtime. You could drop the GPU to a 660ti and save about £80. No SSD as its aimed at gaming performance you can always add an SSD later.