Yet again, the rules of writing rear their ugly heads. Yet again, I have to give a reply that is sure to aggravate some people.
Which is right? ... or . . .? Should there be an extra space before and/or after the ellipsis? What about em dash? What about the final comma on a serial list?
The frustrating part about this is that most of these things are dictated by house style and not by a single right/wrong answer.
Some houses want three periods for ellipsis. Some want no extra spaces. Some want spaces between, before and/or after the ellipsis. Some want you to place the coded ellipsis into the mss, by way of WORD auto-format.
Some houses want you to submit with the em dash already in place. Some want you to submit with -- in place, instead, and they want to make the final find/replace to make them em dashes. Some want spaces before and after an em dash. Some want no extra spaces.
The serial comma is even more confusing. Dropping the final "serial comma" (or Oxford comma, as it's sometimes called) is a holdover from journalism, where space is a big issue. It's less common to find fiction editors who want it dropped, but that does seem to be on the upswing. In fact, several of my fiction editors, quite recently, have told me to drop the final serial comma.
I highly suggest checking the style sheet and/or guidelines for an individual publisher/editor/agent, before submitting and making these things match what is required by that individual. As in all things, do not ignore the diretions given; if you do, you risk rejection and you make a bad impression (sloppy, unprofessional and hard to work with).
If there is no direction given on these items, I would say to err on the side of three periods with no extra spaces at all and to denote an ellipsis as -- with a space before and after (when used in the middle of a sentence to set off a clause), with only the space after (when used as a hard break that leads into another sentence starting) or with no extra spaces (when used as a hard break at the end of a quote). As for the serial comma, I would err on the side of not using it, but as long as you are consistent throughout your mss, it's not going to be the deal-breaker.