Advice for a new journal editor
Here's my advice to you, as a long-time member of editorial boards and, more recently, (co-)Editor-in-Chief: Ask!
Many of us get thrown into this role at one point or other in our lives, and think that we can figure things out, but the reality is that there will be many cases where you simply don't know for sure what to do. In that case, ask around. Ask your older colleagues who've had this role for a while. Ask your editor-in-chief. (In fact, you should have probably asked the questions in your post to your EiC to begin with!) Ask the other members of the editorial board. Don't try to muddle through by yourself, but use the resources you have and assume that the people around you are there to help you figure out what to do.
In addition to this, here are a couple of guidelines you should also follow:
Act ethical: If it is conceivable that a reviewer you have in mind might have a conflict of interest on the paper, don't assign them. If you could possibly be conceived as having a conflict of interest yourself, ask the Editor-in-Chief to assign the paper to someone else.
More than anything else, the reputation of the journal (and, by extension, your reputation as an editor) rests on whether you turn around papers within the timeline the journal strives for. You will frequently assign papers to reviewers who don't respond to your invitation; or who say that they will do the review, but then don't end up doing in a timely manner or at all. Don't let things drag on. Email them again. If they don't respond, call them. If you can't get a commitment from them, unassign them and assign the paper to another reviewer with the request to turn around the review in a shorter timeline (whatever time you have left after the delay). That will occasionally involve calling in a favor from a friend, and sometimes doing the review yourself. In any case, don't let things sit forever -- problems with timeliness don't tend to work themselves out magically.
If you disagree with a reviewer when you make a decision (say, because the reviewer writes a rather short review and recommends publication; but you feel that the review is not of sufficient quality and want to discard it and instead go with the other reviewer who was more critical), then explain your decision. In fact, explain any of your decisions to both the authors and the Editor-in-Chief. People sometimes think of editorial boards as composed of these inscrutable people who nefariously make decisions in smoke-filled rooms based on their current mood; but in reality, editors just do the best they can with the information they have, and then forget to explain their thinking. In other words, whatever it is that's on your mind, communicate it to the people who might want to know, rather than letting them guess.
I'd say the thing that I wished I knew most when I started handling journals is, reviewers are fickle.
- Don't expect that if you invite a reviewer, they will accept or decline. Some never respond. My personal guideline is to wait 7 days before concluding they won't respond and therefore invite new reviewers. You might need a different timeline, depending on your field.
- If reviewers accept, it's not a guarantee they will submit a review. My personal guideline is to wait 7 days after the deadline before giving up on the review ever being submitted.
- Per the above, if you want to be confident that a decision can be made on a paper, you'll need multiple reviewers who have agreed to review the manuscript.
- If a paper is taking a long time to process, the most likely person to remind you about it is the author (sadly).
I'd also recommend getting familiar with the journal office. After all, the journal staff is there to help. If you're lucky, you'll have a motivated desk editor who'll do everything possible to make your task easy, e.g. by configuring the editorial management system to suit you (e.g. what is the default time to give reviewers to submit reviews? What is the default reviewer invitation email supposed to look like? etc), reminding you about late papers, answer questions about processing time, potential special issues, and so on. Unfortunately there are some desk editors who'll simply do nothing unless explicitly instructed ... fingers crossed.
- Check your editorial management system to see if it sends automated reminders at a reasonable pace; if it doesn't, configure it to do so because it's a great help.
- If you have trouble using the editorial management system, ask the journal office. If you want to know statistics like "how long is our average time to first decision?", ask the journal office. There's a good chance the required data is stored by the editorial management system.
- Odds are, as an editorial board member, the publisher will be willing to do you small favours. So for example if you invite a review article or publish an article in the journal, the publisher might be willing to offer free open access or at least discount the price. However, you'll have to ask.
Finally, I suggest making some personal guidelines (similar to the two I mentioned above). Because I was handling so many papers, I found it difficult to remain unbiased. Guidelines helped me treat every paper on an equal footing so I didn't find myself waiting optimistically for a late review because I don't have any other reviewers, for example. I know one editor who waited six months for a late review. Poor authors - they continuously asked, and the editor continuously responded with "it's under review, be patient".
Good luck!