Hi there,
it really is down to personal preference and design, but some ‘standards’ do exist.
Generally do not use pure white #fff or black #000 – tone both down a touch just reduce high contrast. Font size for body: minimum 16px, a lot of people go for 18px.
If you’re not into ‘designer type’ then golden ratio works well:
https://pearsonified.com/typography/
Just add the font size and container width – leave the CPL blank. On the output hover over the font and it will provide the Ratios for your headings etc.