There are easy to follow guides online for overclocking, sometimes step by step. Asus makes very popular Mobos and their BIOS interface is pretty much interchangeable between models, so chances are you will figure it out if you want to try it.
Mild overclocks pose no threat to the CPU, given proper cooling.
Moreso, what "hurts" the CPU is excessive over-voltage, not overheating. CPUs have thermal monitors that will limit voltage or power the CPU down if excessive temperatures are reached, and that thresshold is set to 100oC, which means Intel themselves are pretty confident on the durability of the CPU. Many users go "nuts" for temps going over 70-75oC, but they are simply over-reacting - in my opinion that is.
$500/600 nodes: These configurations are exercises in frugality: how can I have a "render speed multiplier" with the least $ spend, while remaining realistic and reliable. As disclaimed in the blog itself, it is there to provoke & educate you a bit, for you to make your own decisions. Yes, those $600 nodes are great value for $, but remember that after you exceed the critical mass of allowable nodes your Vray licence provides, you have to spend extra just to licence extra nodes. So there is a balance to be kept based on how many licenses you have and how you want to structure your office: 3 workstations with a WS licence each and couple of nodes for each exclusively, without additional licensing?
3 Workstations with a WS licence each and additional floating node licenses so that each WS can use more than 2 nodes (and itself) at a given moment rendering?
Etc.
Does overclocking lower the life expectancy of the CPU?
Well to an extend, yes, it does. But the % of overclock and more importantly the % of over-voltage makes that deterioration vary HUGELY.
At the end of the day, if I can tap into 15-20 or even 30% more performance for the cost of $50-100 or so (typically better cooling and/or perhaps a better motherboard), risking that my CPU will become unstable in the overclocked speed 6-7 or more years down the road...well, I call that a fair exchange, as I would consider a CPU "expired" by that time - at least in a demanding professional or enthusiast environment. Meanwhile, I was experiencing performance benefits unavailable to off-the-shelf products. Before I got my current 6700K, I had a 3930K clocked to 4.8GHz which I was using for a few years (overclocked from day 1 I think). This was a 50% over base speed overclock. It took years for Intel to release a CPU that was out-of-the-box faster than what I had in early 2012...
I would think 4.6~4.8GHz a mild/safe overclock for the 7700K.
Note that this is a very fast clocked CPU out of the box, so 4.8GHz is "just" 15% more than the default base speed of 4.2GHz and ~7% over the 4.5GHz turbo, but it is not bad for a nearly "free" upgrade.
You could go for 5+GHz but that perhaps starts pushing your luck a bit - not for hurting the CPU, but because you are more prone to the "cpu lottery" thing: not all CPUs overclock the same, so you have to be lucky, aka get a golden ticket/chip, that will allow you to push the clock a lot without too much Vcore increase. If you have the time to invest, by all means, try going for more, I just thing the 4.8GHz will be the "easy to achieve for pretty much all 7700K chips with minimal effort" goal.