Need advice for an upgrade

Hey all, 

I built a PC on a tight budget to do everything, its an HTPC, Gaming, Recording and Video Editing rig and now I have a cobbled together system that I have been upgrading as I go and as I had the budget to do so.

The PC sits in the living room and acts like a super console for gaming, video editing and my wife and kids use it for movies and tv. I started to buy bits to get a decent foundation for the next iteration and so currently I have:

Define R4 case

CX450 power supply

HD7850 Graphics Card

GSkill F3-10666CL9D-8GBRL (8 GB, DDR3 SDRAM, 1600 MHz, DIMM 240-pin) Memory (Which is apparently not compatible with my current Motherboard but works so don't know how it isn't)

GA-H55-UD3H Motherboard

i5 760 2.8GHz CPU

and then I have a few hard drives!

OCZ 60gb ssd with my operating system

WD 2TB Caviar Green

WD 500GB Caviar Black

WD 250GB

Seasonic (I think) 500GB

I like to have separate HDD for my stuff and my families (this is pretty sensible) so the 2TB is for my games (steam library of 300+ games and origin, uplay etc) the 500GB caviar black is for video captures, sony vegas etc, I then have a drive for movies and one for tv shows. I wanted to add one for our cd collection but I didn't have enough SATA ports so we now have to do the unthinkable and actually put discs into the dvd drive everytime we want to listen to something. I can't remove the dvd drive or we couldn't rip/watch our movies and tv shows to the system.

I am going to gradually add larger hard drives and will partition them so that the TV/Movies can be on the same drive so that issue will get resolved soon and swap the DVD for a Blu ray drive so we can add our blu rays to a hdd too.

So after all that here is my question. I am thinking that I will be able to upgrade my Motherboard and CPU. I will have to add all my current gear to the system and I will be buying windows 10 when available (currently using win 8.1).

I don't care whether its AMD or Intel and I really want it to be a purchase that will last a good few years, something good quality, well built and robust enough to last and just deal with everything I throw at it. I will add RAM in the future, a better GPU, Blu Ray Drive etc and will love it and take care of it I promise!

What suggested MOBO CPU do you think I should go with given that I will only have around £200 for both? I have been trying to research but its so hard to decide because there always seems to be a "but".

I think the AMD FX 8320 seems quite good for gaming but on the other hand I've read it isn't good for video editing. People say the Intels are great for both however, they are really pricey. I bought a second hand CPU this time around and people say thats a bad idea, is it or would you be happy with a second hand CPU?

I really need some advice and I would appreciate you telling me why you are suggesting the combos you are. 

Thanks so much for reading my never ending drivel and thanks for answering if you can. 

The most restrictive factor is of course your budget. I love my AMD octocore but the Bulldozer architecture isn't getting newer however the price to performance ratio is still there with the AMD option generally be the better value in the all around use-case-scenario.

I buy second hand parts all the time. Just about weekly. The only parts I've had issues with have been motherboards. I'm not saying that is the case for everyone. Just saying. The only bad CPU I got was an APU that got smashed in transit and the guy didn't package it correctly so all the pins on one edge were bent but I sent it back and got a refund. Just make sure you're buying from a reputable sell.