Will my laptop be good enough for streaming and recording video games at 1080p?
probably, but it depends on overall system (laptop) hardware resource load (CPU, GPU, Disk I/O, RAM, etc), which no one can estimate for you
Can I stream/record 60FPS while my monitor refresh rate is 165Hz?
You can, but best practice to keep screen refresh and fps aligned, or at least even multiple. So use 120Hz instead? this appears to become more of a concern/recommended adjustment the closer to maxing out other hardware resources one gets... i think. sorry, not my area of expertise... take others input on this over mine
Will streaming/recording reduce my laptop lifespan or downgrade it?
Streaming/Recording on its own? no.
However, does running any computer at elevated temperatures (from high CPU, GPU and even potentially disk I/O), just like a car engine, potentially diminish lifespan? of course. Business class computers tend to be better built than consumer/gaming rigs, and better able to handle sustained higher thermal workloads (why? simple - typically business warranty is 3 years vs 1 yr for consumer PCs... cheaper for OEM to avoid warranty issues with slightly better build).
Will any of this matter to you, especially as a gamer where you are likely to replace laptop in 3-5 years? probably not... unless you are running near thermal limits for many hours a day, every day. But there is no hard line. You could run a system hard for years and not have a problem, or you might only not stream/record at all, and still have a hardware issue.
If my laptop can stream/record, what's the recommend settings?
Start with auto-config settings and go from there. 'Optimal/Recommended' Settings will vary based on background processes, level of Operating System and OBS Studio optimizations, game workload, and more. Get your Streaming/Recording working, then worry about optimizations later as you determine your requirements (there are often compromises across various OS, OBS, and other app settings, performance, output) and expectations. Some games may require different settings. sorry, but the true answer is... it depends
I'm really new to streaming and hoping to get some help, ty!
Good luck on your journey.