Summarizing all you folks recommendations and advice, I have decided NOT to procure used parts. There are 2 reasons mainly:
1) Quality assurance; it is very hard to tell the actual condition of the part, how to test and RMA is not possible in case the results turn out to be negative.
2) Hard to justify the price of the items; a used i7 might be pricey than a brand new i3 9100F. And the prices vary greatly.
I have decided to go for a NEW system, with some room for future upgrade. The scale of the upgrade will be platform dependent. What I mean is two options are being considered, one being the AMD platform, the other is the INTEL's.
The route is based on the justifications of price, upgrade-ability and the game genre which I play mostly.
I appreciate the idea of going for AMD because of its future proofing more or less, and the backward compatibility offer which I think is a genius strategy by AMD. The PS5 and XBOX's deployment of Ryzen CPUs also affect my decision here. As mentioned in previous thread, politically future games will be driven by these two game vendors. 8c16t definitely is the trend to go beginning in the fall of 2020, that is a little more than a year and a half away. BUT, there is still some time here and maybe AMD will offer more flexible chips and chipsets during this 18 months. Therefore, a more balanced approach is to select a CPU which is just less than 50% of usage across most of the AAA titles predominately BFV, The Honor and FFXV. I would also be looking at some other up coming AAA titles most notably the COD. After watching over 50 videos in the last 3 months, I have observed that even a 1600X can reserve much room when running at Ultra settings coupled with a high end GPU Like the RTX 2080 under 1080 gaming environment. This highly suggests that modern games are more GPU dependent rather than CPU bounded.
It is also undeniable that Intel 9th gen is sort of coming to an end. The lethal factor is the frequent release of next generation products and the minute difference between consecutive generations. The difference between the 8th and 9th gen CPUs aren't really significant. And the removal of additional thread evident in the i7 9700K is hard to comprehend. The attitude of Intel also displays to the community an impression that we should all spend more to get additional cores and threads if you want to gain more FPS. Otherwise you're not left with much choices. This arrogance has caused some frustration and dissatisfaction within the community and further divides the factions. At the same time, the horsepower delivered by Ryzen 3 line of CPUs has catalyzed the shift towards the AMD side, some die-hard Intel fans have in fact defected. BUT, still if you want a pure gaming machine, Intel's proprietary IPC really has its superiority over AMD's, at least for the time being. And the base and boost clock frequencies still prevails. Tens of side-by-side YouTube video game benchmarks show that highest FPS is dominated by Intel at the same core clock.
Integrating all of you folks positive recommendations, I have therefore drafted up the followings
AMD - B450 platform AMD - ZX570 platform Intel - B365 platform Intel - Z390 platform
Ryzen 3 3200G 3.6-4Ghz 4 C/4T 12nm Ryzen5 3400G 3.7-4.2Ghz 4 C/8T 12nm Core i3-9100F 6M Cache up to 4.20 GHz Core i5-9400F 9M Cache up to 4.10 GHz
Stock Cooler Wraith Spire Stock Cooler Wraith Spire Corsair H60 120mm AIO (2018) Corsair H60 120mm AIO (2018)
Asus ROG Strix B450-F Gaming Asus ROG Strix X570-F Gaming Asus ROG Strix B365-F Gaming Asus ROG Strix Z390-E Gaming
Corsair Vengeance LPX 3000 CL15 2 x 8GB Corsair Vengeance LPX 3000 CL15 (Black) 2 x 8GB Corsair Vengeance LPX 3000 CL15 (Black) 2 x 8GB Corsair Vengeance LPX 3000 CL15 (Black) 2 x 8GB
Corsair RM 750W Corsair RM 850W Corsair RM 750W Corsair RM 750W
Please recommend good NVMe and case