It is very difficult to detect the virus especially if it was being hidden by the mining software that you have downloaded. Antivirus is your only option to detect them so it will be best if you will install the top ranking antivirus in order to lessen the chance of any virus to bypass it.
It is, actually. Remember that we're specifically talking about mining here. It's easily easily noticeable if your device is unusually using up too much unnecessary power especially if you aren't even doing anything that resource-heavy.
It would surely use more than 70% of your CPU's power and graphic cards power because the virus is taking your computer's resources for themselves this kind of problem is a common issue regarding what does the virus does to your computer, and surely prevention is better than cure but what if it bypasses that prevention most of us are talking about, I think this kind of Virus can be removed by Malwarebytes, you can surely double-check it just to be sure and you can even reset your browser in a default settings as well.