What do you as an "interface designer" do? Do you need the complex computational power of an i7? If not, then the fastest i5 should do.
It's always best to get as fast a CPU as possible - for the future when more complex OSes take more computing power. So while you may not need the power of an i7, you probably wouldn't want an i3. Which would you rather buy, the 2.7GHZ i5-6400 for $180 or the 3.3GHZ i5-6600 for $210?
http://www.pricewatch.com/price/cpu/i5-6600 If you're going to supply your own heat sink solution then the 3.5GHZ i-5 6600K can be bought for $218. Chances are you wont be over clocking it to almost 4GHZ, but just having the faster cores should be a benefit. Some guys like the $30 coolers (like the Cooler Master 212 EVO for $30, for example. I prefer the $70 Noctua NH-U14S for it's better quality, superior mounting system and quiet fans. Some had Skylake CPU wafers breaking, but I tend to attribute it to the heat sink mounting system that they bought into.) When it comes to choosing between a loose bin CPU and a Retail version, if the price is the same always go with the Retail version, even if you will not be needing the stock fan. Intel fans are darn good, btw. Their mounting system leaves a lot to be desired, though.
It's always best to buy a mobo with 4 RAM slots and populate all four slots in quad channel for the greatest mem throughput. If you have your heart set on 16GB then four 4G sticks should be relatively inexpensive (up to the point where they are no longer produced - then the price goes up as old stock becomes scarce.) Selecting RAM is a science, and one starts at the mobo manufacturer's Certified RAM list. One compares prices for various timings and comes up with the best "bang for the buck" choice.
If you are going to always leave your PC on then you will probably need a PSU that can handle Hibernation and Deep Sleep, so a Haswell Certified PSU is always a good idea.
As you research your choices read the user reviews at Newegg and Amazon to get an idea of what problems others have and temper it with the knowledge that it may have been due to their choices of incompatible parts, their ignorance, etc. Compare the time line to when revisions were made, things like BIOS updates may have fixed a problem, or Quality Control was beefed up, or the manufacturer changed suppliers, etc. Whittle down the data so that you get a clear idea of what the hardware problems really are. Typically I start with the most reviews and work my way up, dismissing obvious user errors. Look at the spread of Ratings. If a hardware piece has more negative reviews than positives you may want to deeply think about not buying it. Whatever hardware you're are researching do Google searches for that piece with "Review" and "Problems" filters. While you are not likely to read too many problems with computer cases the Reviews should point out any obvious problems.
While you may not need the fastest CPU and the fastest GPU, if you do a lot of Internet surfing, the greater the RAM you have and the faster the video card, chances are the smoother your surfing will be - things like watching YouTube Videos and keeping many browser tabs open, for example.
Chances are that if it is work related you will want as quiet a PC as possible. May I suggest that you rip out all the fans in whatever case you buy and install Noctua fans? They're expensive at $15 (120mm) - $22 (140mm) apiece but, IMO, are well worth it. Yes, even SSDs need cooling since most have thermal circuits that degrade performance if they start over heating.