The easiest way to differentiate tiers and generations of personal computers is the chipset/ CPU, ie z97, x99... ect. Once you're comfortable with the technology that fits your budget and needs you'll be able to separate all the other components much more easily.
Picking the right motherboard is a lot of dancing around specs and requirements for everything you've justified down the line. Really, not a lot to say here except make sure everything's accounted for. After you've established the minimum of what you need it's easier to think of what you may want. Then you might justify another tier based on a few options you'd prefer, like audio or components suited for overclocking.
HHD/SSD is simple. All your programs and games should be installed on your primary drive so I would pretty much stamp that as a 250GB minimum SSD. I might even try a 10k RPM HHD if I had one lying around. Mass storage is less of an issue. 7200+ RPM is something I'd shoot for where 5200 is going to be your bargain price point. Nothing really changes going up the dollar tree on this one accept the quantity of each and various Raid configurations.
Single video card is nothing to worry about either. Pretty much get what you pay for. I prefer nVidia and would not get anything less than their x80 model from any generation. Mostly a personal tier of performance based on a 2-3 year or half system life upgrade. Your choice of graphics card can make or break a modern system's potential in gaming. More so than a few small bumps in other places.
I generally wouldn't recommend 2 video cards to anyone outside the very top tiers of performance where the best single card commercially available is doubled or more. ie I would not tell you to buy a 970 with plans to add an additional card in a short period. If you do plan on sli or crossfire you need to essentially double the Amperage requirements given by the card and make sure your pci-e configuration is going to be supported on the mobo.
Power requirements can be calculated pretty accurately with a full cart from your favorite retailer. You can find wattage calculators online that take all the odds and ends into account, but make sure to include the efficiency of the PSU into your final calculation (multiply by reciprocal of PSU efficiency for true wattage requirement). The most hefty requirement and easiest way to lvl the field is the amperage on the +12v rail for any dedicated video card of merit. You'll find that the recommendation is usually around 42-48A @ +12v and is based on a system with lower than average draw for gaming. From my experience, this will not be satisfied by anything less than a decent 600watt.
Computer cases in an air cooled system are as important as anything. Keep wiring trim with modular power supply and hope that you didn't go too cheap. If you do encounter heat problems adding some fans or re-applying paste correctly can do the trick. I personally run all my 3-pin fans off of the power supply directly using 3-pin to molex adapters. 3-pin fans are 'gas n' go' so wiring them through the board isn't necessary. Where 4-pin fans should stay connected to the board with the 4th pin controlling the rpm via software/ firmware.
Memory can be tricky. First off RAM speeds over 1800Mhz have been reported widely as giving a nominal gain in performance for gaming. You'd basically need to run out of ways to spend money before you cross that threshold in 2015. Refer back to chipset/ CPU for any possibility of making use of a multi-channel set-up as the performance gains are practical. I always fill my system (multi-channel lots) at the time of purchase because using a matched set can prevent issues of compatibility in heavy draw applications. ie if I had a quad channel supported system I would buy 4x8GB quad channel supported memory in place of 2x16 or any other config. Memory timings and fancy heat sinks are going to be the premium in price between similar specs. You can play around at the bottom of the barrel, but good RAM will be synonymous with stable. I've used Corsair for 10 years so I can't comment on what's out there.
I say try again. Do a few builds where budget is higher so you can just make everything work together. When you get a little more savvy is when to pull out the chop saw. To justify a new computer for gaming I'd need to run the most contemporary pain in the ass to run game @ 1080p, 60fps solid, all post processing features at medium to high, with 4x filtering. It may be a hefty demand or it may not, but in just over a year it'll be the 5/10 average requirement in AAA games. After the second and third years you'll be feeling the strain and you want the flexibility to say all I need is a new video card. Start out on the right foot.