First thing: Don't stress yourself out. This project is supposed to be fun for everyone and a burden to no one. Let me share a little story before answering your questions...
When I was a kid, I loved spending time in any swimming pool, especially if it had a diving board. Seeing this, my parents enrolled me in diving lessons. Well, my instructor apparently saw potential and began grooming me for competition, filling my lessons with more and more complex dives. I'd go home absolutely exhausted! Suddenly, diving wasn't fun anymore. I eventually quit his class and never looked at diving board the same way again.
Don't let this happen to you.
Okay, now for your poetry book...
The first thing you have to do is start collecting your stuff. Before I published, my poems were scattered both online and in various files on my computer. It was quite a task to scrape 'em all together into a single directory.
Once you've got 'em all in one place, decide if you have enough for a single or multiple volumes. My first book is about 12,000 words and my second about 18,000. As you collect them, consider how they can be arranged or categorized in your book. Then, once you have 'em all together, begin copying/pasting them into a single VERY LONG Word document into appropriate groupings. A work count on the finished product will give you some idea how to proceed regarding the number of books to publish.
I don't know how long/short your poems are, but I tried to mix my longer/shorter works evenly throughout the book.
Times New Roman is a good, all purpose font that translates well for all eReaders. I prefer 11pt. as my default, but many people prefer 12pt.
If you're comfortable with the order of your poems, cut/paste the titles in order to the top of the document. This will be your table of contents.
Too many graphics can be problematic in an eBook; a picture that looks good on a Kindle Fire may not fare well being squashed onto an iPhone. Unless they are absolutely necessary, graphics should be kept to a minimum. The only exception is the cover graphic.
Guess what? At this point you're already passed the halfway mark in publishing your eBook(s)! How 'bout that?