CAD/GAMING Build ($900/PHP 45000)

On Overclocking and using an Overclockable CPU on a non-OCable MB
You'd OC mostly for gaming, not much for productivity works -- but it does help esp. during CPU rendering (faster time).

The point about the CPU + MB pairing is: if you are going for the processors you listed (i.e., i7-6700k/i5-6600k/i5-7600k), you'd be better off at a price/performance standpoint in getting the non-K versions (i7-6700/i5-6600/i5-7600) to pair with the motherboard you were initially considering (i.e., B150m mortar/Gigabyte B250m).

For example, the i7-6700K, non-OC'd works at 4.0GHz (base clock) to 4.20GHz (boost clock) at 91W TDP which sells for $290 (or Php 16,940 in the Philippine website I linked). On the other hand, the i7-6700 works at 3.40GHz (base) to 4.0GHz (boost) -- just a mere 200MHz difference from the K-version -- but only at 65W TDP and sells for the same $290 in the US (but only Php 15,300 in the same website in your country). That's a savings of Php 1,640 for almost the same performance in non-OC use, lower heat, lower power consumption, and, not to mention, already has a stock CPU cooler you can use out-of-the-box (unlike the K versions where you NEED to buy an aftermarket CPU cooler as it doesn't come with one -- that's an added cost).

Same goes for the i5-6600K: 3.5GHz to 3.9GHz at 91W and $220 (Php 11,750). But the i5-6600: 3.3GHz to 3.9GHz at 65W and $210 (Php 10,950). Again, same performance at non-OC use, lower heat/power consumption, including stock cooler and Php 800 less.

i5-7600K: 3.8GHz to 4.2GHz, 91W, $230 (Php 12,190); i5-7600: 3.5GHz to 4.1GHz, 65W, $215 (Php 11,200). That's only 100Mhz difference (same performance in non-OC), lower heat/power, stock cooler and Php 990 savings.

So, in short, if you do not intend to OC, you are just wasting money getting a K series CPU and pairing it with a B150/B250 motherboard.

On Ryzen or Intel CPU
The Ryzen 5 1600 I suggested would be definitely more ideal for the PC usage you mentioned (and so is the Intel i7). The i5's (with 4 cores and only 4 threads due to the lack of hyperthreading technology) are mostly geared towards a pure gaming PC, which in your case, it is not.

The 1600 has 6 cores and 12 threads (very useful in your architectural rendering and other workstation usage). The i7-6700K and the i7-6700 (non-K) both has 4 cores and 8 threads (also useful for workstation use). Here's a direct comparison of the Ryzen 5 1600 and the i7-6700K: http://cpu.userbenchmark.com/Compare/Intel-Core-i7-6700K-vs-AMD-Ryzen-5-1600/3502vs3919 . Take a closer look at the Workstation effective speed as this would be your primary use for your PC. In terms of gaming, the i7 still has the clear advantage in single-core speed, but, the 1600 is not that far behind. Here's another review of the Ryzen 1600/1600X and how it fairs with the Intel counterpart: http://www.techradar.com/reviews/amd-ryzen-5-1600x .

On 4GB RX 580
Yes it is, especially if you want to shave off some more costs. The 8GB is only ideal if you want to max. out most games on a 1080p/60Hz monitor. The 4GB still does a slightly equal job, but, it mostly depends on the game and your in-game graphics settings. Consider the 4GB if you want to save Php 1,600 on the GPU compared to the 8GB version. Both are still better than the GTX 1060 3GB.