There is no magic answer.
Just return a certain amount to you , I think, enough.
In my user interface, I have even seen feeds that return 1 (one) element. Like those that return ~ 100.
I think the number 20 is a good compromise.
In addition, you can rely on a period , not a specific number. In this case, you could submit feeds added from the last 24 hours, for example.
zerkms
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