The best place to start is in the buyers guide at the front. Its there for this reason. Stick to the guide and you will have a working machine. When you deviate from the guide because you saw this really cheap motherboard, CPU combination at your local flea market that no one else has ever seen, then you will suffer pain and disappointment.
Many people have built one machine, quite a few more than one, very few will have built the specific machine you want so will be unable to say buy this and that and keep it to 900 CAD. You say you are tech savvy, this should be easy. Sticking to the parts and reading and reading and asking specific advice will help. Asking general advice is fairly pointless.
My general advice would be that if you want to go gaming and video editing the graphics card will be a major component of your cost. If you choose FCP X then the AMD cards rather than the nVidia are best but the AMD cards are not so hot for gaming. No idea about non FCP X as I don't use anything else.
You are better off if you work out the specific software you want and see what the publisher suggests for hardware (specifically about graphics cards) and then work from there. Never assume that because one graphics card does X,Y and Z, that the next one up or down in the range does the same or even similar. I brought my kit based on specifications down to specific vendors exact SKU. I didn't buy 32GB RAM, I brought Crucial 32GB part no 1212121312e3asbcjkasddfioudioascxas (or whatever it was). I knew that combination worked and never assumed anything.
I would suggest that you choose your parts, work out a list and post specific questions. If you choose from the list you will have a working system. Deviate and you're lost.
