The "large" thumbnail option gives you a bit more width for your caption wrapping. This is just a caption, FYI, not the "show attachment title" value. I don't personally love the way "show attachment title" looks, but you do you.
Embed captions "wrap" to a fixed maximum width and minimum height. You can exceed the minimum height, but not the maximum width. Be disciplined in your writing or these will become visually unwieldy.
This is the “primary didactic panel” of your exhibit, like the text you first read when you enter a physical exhibit. The goal for this section is to set up the "narrative arc" of the exhibit and to set the stage for the connections you will draw between your curated artefacts and the story you wish to tell. The length for this section is up to you, but we’d suggest around 350 to 500 words. The exhibit itself should have a memorable title and this text should serve as a “hook” for the audience — they need enough information to understand the overall story of the exhibit, but you also want to leave them wanting more.
Embedding 1-2 images in the intro page is optional but encouraged. Doing this is slightly fiddly and involves placing “media embed” blocks before, after, or between the “HTML” blocks you are using for the text itself. This can involve a little trial and error to determine where the best place is to place the “embed” block so it appears where you want to in the accompanying text. Embeds give you the option to “float right” or “float left” the image — this tells you what margin of the page the image will appear on. It also gives you the image to define roughly how large you want the image to be, and whether or not you'd like to display the image's title or a caption. It's up to you! But remember you need to attribute all the images in the exhibit somewhere — see the example "bibliography" page for more information.
This is a picture of chickens. I ran out of downloaded pictures from that book of hours. Plus, chickens are hilarious. Chickens! Ha ha ha. See how this too-long caption looks weird dangling beneath all the other text? Maybe don't do this.
Placing embeds involves a little trial and error. Feel free to play with the "layout, "media display," "image type, "and "show image title" values to see how they affect the placement. It can take a little time to get right, but it’s worth it to break up the visual monotony of a lengthy text block. The internet’s attention span is measured in nanoseconds; the more you can do to counteract people’s instinctive tendency to recoil from reading anything longer than a Tweet, the better off your exhibit will be. The good news is that all elements within an Omeka are drag-and-droppable, so it's easy to adjust the placement of visual elements.
For reference, this text is 444 words in total — about the right length to aim for. But remember that it’s up to you to decide the most effective way to tell your story! But as you work through the design process, especially if you're embedding images, you might find you wish to make some paragraphs shorter or longer so they will work better visually with the images you've chosen.