Yeah store bought is always a mistake. A blind monkey could put a computer together , the only tricky bit is getting the cabling neat, but as an electrician you should be fairly good at that.
That is good, putting them together is fairly basic. Most things are 'keyed' so you can only put them in the correct way. The hardest part is probably choosing the parts.
Sure thing. Trying to figure out a couple things and then muggs said he would do it. I can let you know once he does, as it never hurts to have a second opinion.