I currently have a amd r7850, 4gb of ram(had a stick die) , a amd a8-3870k and a asus f1a75-m, Windows 7 (64bit) and the other stuff hdd good 1080p monitor. I use it for gaming mostly. (A lot of new games)
Firstly, forget about the fx-6100. Get a 6300 or 6350 (if the 6350 is on sale its the same price as the 6300) they are both newer and better than the 6100, and almost the same cost.
Yes, that motherboard will fit in your case.
If all you are doing is gaming then 8GB is plenty so just get 8GB (Ram is expensive because there was a fire in one of the main factories that make like a third of the ram we use in desktops, or something like that, point is, get 8GB now, you can just always pop an other 2 sticks in later if you wish )
YES, SSDs are worth every penny, (I'm in england) In my opinion an SSD is the best value upgrade you can make to a pc. I personally have a samsung 840 120GB ssd and I have never regretted buying it, it just makes my pc so much nicer overall.
As far as your last question goes, I'm not sure I dont know a lot about games and gpu performance that so I dont want to give you the wrong advice.
Just get ram that is the same frequency, and cas latency and same voltage. brands dont matter (besides from looks, i have 'mix and match' ram and it works well (actually right now i have 3 dimms in a dual channel board but it still runs in dual channel luckily (i had ram die recently too) and it looks ugly and ridiculous. but it works :D
Also that stupid LE one doesnt even have a heatsink next to theVRMs, just get the M5A97 R2.0 board. I personally have an FX 6300 and the M5A97 R2.0 and they work out of the box and its a pleasure to overclock with them
Yes, that will be perfect for that setup. You can search Google for a "pc powersupply calculator" and that will give you minimum and reccomended wattages for all sorts of setups
If you can, try to find a single 4x1GB stick from the same brand, with the same clock speeds and timing. That'll give you the best chance of the RAM working well together. Theoretically, RAM with the same clock speeds and timings should work, though.