You've got the right lesson then. :) Make a budget and stick to it where most of your money is going to go into graphics and mobo-cpu. I never recommend skimping on any of those components. Did you plan to reuse or have you included the case or monitor? They aren't that expensive but I've seen budgets busted because they forgot to include these fundamental parts.
As a side suggestion, I would recommend staying away form AMD if this is your first machine. If you had experience with building machines but otherwise I would stay with Intel for your first system.
Support should allow Carry to get last hits on creeps as much as possible to accelerate their growth. I have found that playing Support that it is beneficial to focus on creep Denies over Last Hits help out Carries better than other stances stuff like interference.
But Silicon Knights have a history of over-promising and then blaming everyone but themselves on their failures. People are rightly skeptical where suggesting they are just bandwagoning ignores their actives that go all the way back to 2005~.