Ro,
One of the things I've learned is that different people do things differently. For example, one person says to not use any contractions when writing. Others say that it makes for more readability, so please do use them.
When I published my 3 books, I looked at the Chicago Manual of Style, as was suggested by one of the publishers. The style of writing (grammar, punctuation, etc.) changes every year, I think it is. The book I looked at was the 15th edition. Everything keeps on changing.
Although I did as they showed to do for commas, it looked strange to me. They'd said to use a comma after each word of a series of words. Sometimes (or some years), you're not to use a comma after the last word of the series. It seems to look better (more pleasing) to my eyes to not have that last comma, but I did it the way they said to do it, anyway.
The old saying which goes, "You can't please all of the people all of the time," seems to be true in the writing industry.
Another thing I learned through studying that manual was that a person should be uniform in the way they use numbers (whether using the numeral or spelling out the word) within the same paragraph. So, if I'm using the number 10 for example in a paragraph and also the number 15, I shouldn't spell out one of the numbers and use the numeral in the other one.
So much to learn...so little time.
Ann