Please suggest ideal or best text size and font of content of posts in entry-content class in mobile devices (less than 400px width – say 360 or 320 px width)
this really depends on the font being used as there visible size varies.
One rule is they should never be below 16px as google may flag a ‘text too small’ warning.
The 17px you’re currently using looks great. If you’re concerned about short lines lengths then reduce to 16px.
if speed is important then i stick with System Stack.
For technical/academic blogs i generally stick with Sans fonts – such as Open Sans or Noto Sans. Headlines i quite like Montserrat.
To replicate the google news feed swipe to remove – would require custom development. It would be quite complicated as well.