Learn English – Changing from 1st Person to 2nd Person in the same paragraph

This is purely a matter of style. Even Dickens' publishers didn't follow that rule. This is from Google Books' reproduction of A Tale of Two Cities published in Philadelphia in 1859:

However, at least one reproduction of this passage does split this single paragraph between the end of the quote and And.

Paragraphs generally hold a single idea. If there is narration which follows directly from the quotation and it could be understood as part of the same idea, it's reasonable for it to be all in the same paragraph.

Traditional RP has 12 monophthongs: six short vowels—kit, put, dress, strut, trap, lot— five long vowels—fleece, goose, nurse, thought, start and the schwa—banana.

According to this blog post, Modern RP has up to three more monophthongs—square, near, cure. These are essentially long versions of the short vowels dress, kit, put. However, it also says that in modern RP, the vowels in fleece and goose are turning into diphthongs. But I suspect that a lot of speakers don't follow either of these systems exactly. So this gives 15 vowels that might be pronounced as monophtongs in RP (some of these are long and short versions of the same vowel), and 10 vowels that generally are.

And the number of diphthongs isn't constant in American English, either—the vowel of ride is often a monophthong in Southern American English.