1) Is there a way to make the Caption field in the Metadata panel larger?
Yes. You can select the “Large Caption” view from the drop down menu in the Metadata panel header (to the left of the word Metadata).
2) Are an image’s Develop Settings saved in the metadata of an image?
By default Lightroom saves changes made to an image in the catalog. I would suggest, however that you also choose to copy the information from the catalog into the individual files. To do this, either check “Automatically Write Changes to XMP” in Catalog Settings > Metadata and/or select Metadata > Save Metadata to Files when finished editing images. Either way, the Develop settings will be saved in a sidecar file for proprietary raw files, inside a DNG file and inside a JPEG, PSD and TIFF file if you have enabled “Include Develop settings in Metadata inside JPEG, TIFF and PSD files” in Catalog Settings > Metadata.
3) Is the History saved in an image’s metadata?
No, the History (in the Develop Module) is saved only in the Lightroom catalog.