There really isn't a "best BIOS" settings as it will vary heavily per user needs as well as their hardware limitations.

You don't have to change every setting in BIOS, you could more than likely leave it how it is now and be more than fine. With that said, one thing for sure is to make sure XMP is enabled. Seeing you have 3000MHz RAM, make sure XMP is enabled. Some motherboards don't auto-enable that setting where your RAM will be at a lower speeds such as 2133MHz.

If you care about fast boot, there should be an option to enable fast boot. This makes it so you load into your PC quicker, but if you need to get back into BIOS, can become a hassle if your keyboard doesn't receive full power quick enough.

As for overclocking, if you've never overclocked before I highly recommend you watch some videos before trying it; however I would caution about trying to mimic those videos. CPUs are different. You can have a CPU that is normal and will OC like it should, you could have a CPU that is a god tier and will OC easily 0.8 or higher than it should and remain stable or you could have a CPU that will not be stable with an OC at all. These things happen, so your best bet is to tweak around settings slowly to see where your CPU is at.

Also for keeping your PC cool, that's going to rely on your fan setup inside the case and the ambient temperature around you. I normally refuse to use BIOS for fan control as I hate the fact that I would have to go and out of BIOS to change the fan settings and depending on how the day is, I will be changing fan speed constantly. Some motherboards have software that allow you to control your fans from your desktop; whereas I just threw in an NZXT Sentry 3 to control my fans from outside my case. If you have good ventilation and a decent aftermarket CPU cooler whether air or AIO, OC'ing your CPU shouldn't raise your PC temps crazy high. However if you're forced to use BIOS for fan control and you aren't too concerned about fan noise; I would say 50-60% speed would be a good enough area to keep things cool, at that point I would also advise you set a fan curve for your GPU through MSI Afterburner or whatever you're using to monitor your GPU with.

Please tell me you didn't actually pay £120 for a GTX 750Ti.

As for overclocking, you can use the Ryzen Master utility within your OS. Max voltage for Ryzen is like 1.425v I think. I've seen some people with 4.1GHz stable on R7 CPU's with 1.45v though. I'd just set voltage to 1.4v and clock speed to 3.6GHz, and then start adjusting both clock speed and voltage slightly, as necessary.