It's pretty good, I think it will be fine... EXCEPT one thing. The power supply. 450 watts may be OK, but, you're not leaving yourself much room there. If you can scrape up another 10-15 bucks and get a 500 watt or a 550 watt, that would be better. I wouldn't try to build a gaming computer with any PSU less than 500w, although it is technically possible. The extra wattage will also make it more efficient, power supplies tend to be less power-efficient when they have to run closer to max capacity.
But the Ryzen 5 1600 and the GTX 1060, that should be a good match. The motherboard is suitable, I usually buy Gigabyte motherboards and they have always been good for me, I have one still going after 10 years. And 8GB ram is enough. You should be able to run almost all games out there, maybe not at max settings with the very latest stuff, but that's fine, because most of the interesting stuff isn't the very latest stuff anyway.
As for buying used stuff, well, be careful, it could be a good option in this case, but make sure you can claim on that warranty if there are any problems.
And, advice for everyone, be careful plugging in graphics cards. Make absolutely sure you're using the right plug on the PSU, in some cases a wrong one can look very similar, but it will instantly fry the damn thing.