Motherboard Purchase Question

Hi all. I just recently stumbled across this board trying to pick some brains. I was recently given a maybe five year old Dell tower (I couldn't tell you model as it's at home and I'm at work) that I would like to upgrade piece by piece. Now I would consider myself computer-savvy. I can easily master all of the inner workings of Windows and Linux and have fiddled around with OEM Bios' before but unfortunately I have never built a pc and don't know everything about the insides of them. Is it even possible to piece together pieces or will they not play friendly?
I was thinking about getting a motherboard/cpu combo in the $100-$150 range withen the next day or so such as either the ASRock E350M1/USB3 AMD E-350 APU (1.6GHz, Dual-Core) AMD A50M Hudson M1 Mini ITX Motherboard/CPU Combo or the SAPPHIRE PURE Fusion Mini E350 AMD E-350 APU (1.6GHz, Dual-Core) AMD Hudson M1 Mini ITX Motherboard/CPU Combo. I'm kinda leaning towards the Sapphire but I was wondering which is better or if there is even something even better in that price range (USB3.0 is a must).
Also, I noticed the Sapphire uses 2×204pin SO-DIMM for memory. That is essential laptop memory, no? Anything else I might need to bring into consideration?

Thanks for any help.

p.s. Unfortunately I am unable to post links but if you are kind enough to copy/paste the item description I'm sure the newegg product would be #1 on google.