I agree with the i5 vs i7, but disagree on building your own computer causing problems.
As long as you get quality computer parts built by quality manufacturers from reputable merchants you'll have less issues than with pre-built PC's. I've spent no amount of time working on issues. In the off-chance you receive a bad product you can easily figure it out by unplugging components until you isolate the problem child.
I use Windows 7 and love it. I know a lot of developers such as Valve have condemned Windows 8 as a gaming platform. Good to know you haven't had any issues.
I'm just saying there is possibilities hardware/software issues which are pain in the butt solve sometimes. It helps to have access to multiple computer/parts to find out what is bad, if on the slight chance it happens.
Going with what you said on RMA issues with Asrock motherboards, I may have to agree with you. I built my own computer with an Asrock Mobo(stable since Sept 2012), so I decided to put that into my cousin's custom built. It seems that he has an issue with the Ethernet network connection breaking randomly. I'm thinking it might be a router issue or motherboard's Ethernet port is defective. This is just one example of a computer that runs fine, but has random problems you need to solve. HalfAmazingOne, I wish you luck in avoiding problems such as this and hope you enjoy the savings/building process.
Regarding buying a computer case, I would recommend getting a quality and easy to use computer case. Try to ignore the higher initial costs because cases last forever, the case will be easier to clean/maintain, and be easier to install parts into.
Corsair 550D $149.99 with $10 rebate [newegg.com]
Fractal R4 $109.99 [newegg.com]
I personally worked with both cases. They are easy to clean because they have fan filters at all the intakes and have plenty of room inside to fit everything. You definitely want fan filters for all your air intakes for case because you definitely don't want to clean out your every couple months to remove all the collected dust. It's much easier to take off all you fan filters every month, wipe them off in the garbage, and be done with cleaning your case.