I do wonder why more writers are not using Vim as their daily editor. As a piece of software that has existed since the 1990s, Vim has created an arms race for human beings who have deemed that the only correct way of writing text is by doing it at break-neck speeds.
The ability to manipulate text with insane levels of efficiency might have been one of those triumphs of our species that has flown over most heads in the past few decades. Story-telling is central to humanity and thus how we compose those stories and convey them to others is important. Vim is thus important.
Here are some important motions to aid you on your journey.
Changing words
We can use cw to delete from the current cursor position to the end of the current word and enter Insert mode. ciw is even more useful when we want to change the current word, even if the cursor is not at the beginning of the current word. diw, yiw and viw also work here to delete, yank (copy) and view the current word respectively.
f, F, t, T or just search?
Because we use many letters very often when writing large sections of text, it may be more efficient to use /word+Enter to jump to the word to be changed and then use cw.
f, F, t and T (and ; or , for cycling between characters) are more suited for scarcer characters such as periods and parentheses. These are more suited for coding where the special characters are common.
Changing a sentence
Yes Vim can select sentences. vis can be used to view the current sentence that the cursor is in. cis allows you to replace the sentence. If you want to change everything in the sentence after the current cursor position then using ct. (change to period) is the better option.