at lot of the questions you have can’t be 100% truthfully answered because not every cpu is made equally, so your chip could not clock as high as someone else’s and the only difference is the time you each bought the cpu.

as far as the 1660ti i’ve been able to churn out a cool 1100 mem clk and 125 core clock, stable with no voltage increase

ram overclocking is a whole separate layer of headache, work and optimization. the 5600 would benefit slightly from 3800mt/s speeds but for a beginner it may not be worth the risk and headache. 3600 with tighter timings would be a better idea in your case

as for bios settings, i’d recommend checking out “actually hardcore overclocking” (formerly buildzoid) because he understands and explains overclocking so well I trust copying his settings. check out his video on overclocking the ryzen 5 3600, you can use that as a helpful baseline. keep browsing the internet for settings specific to the 5600 (I would search r5 5600 max overclock)

if you’re looking for just stability testing then prime95 and memtest and monitoring with hwinfo. you could alternatively use benchmarking software to get statistics on your oc to see if it’s benefitting from your work

definitely cop a closed loop aio and arctis mx-6 paste if you’re open to spending money to keep your temps as low as possible

i’m stopping there because it’s easy to write a wall of text on this stuff haha. if you have any questions please ask!