@RiidDisBuk Hello!
First question:
Tapas allows a total of 15,000 words.
For a regular published work, the recommended is 3,000 to 5,000 words.
The average is 2,000 to 2,500.
Second Question:
You're totally fine!
Most people are reading on their phones, which is why it's recommended to keep chapters short. This is what Tapas recommends.
A lot depends on your writing and updating schedule. So if you're doing bi-weekly it's okay to post 900-1,110 words. If it's once a week I suggest you stay at or above 1,500 words to keep your readers pleased.
At the end of the day as long as you're consistent with updates, it's okay to post short chapters.
If your readers love you, they'll stay. My favorite writer wrote less than 900 at times, and while I groaned whenever I finished the chapter I always waited for the next anxiously and cheered him on.