Would like to be a angel investor

I am exploring investing and in particular in startups, I’m a full time employee. I have some initial questions that I hope you can help with.

Regarding EIS/SEIS - if I were to invest in startups that are eligible for these tax breaks how long do I have to hold the shares before I can get the benefit of the tax breaks?
in my situation how would I get those tax breaks in practical terms i.e. do I need to contact HMRC and inform them? where can I find out the process?
I’m aware there is Loss Relief for capital investments in startups, how does one qualify for that? would I qualify for it? I read somewhere you have to be in the 45% taxband to qualify, I pay 40%?
Look forward to your reply, Jzkallah khair