I use Adobe Lightroom to catalogue and edit my photographs, and export to the desktop for uploading to Later. I know that there is a plugin/service [for the moment at least] which can be used to post direct to Instagram. I love the scheduling of Later, so that's not an option for me. The one thing that I need is the ability to add captions in Lightroom which are recognised by the Notes / Caption area, of Later. At the moment, despite being added in various IPTC fields in Lightroom and showing up when exported, they are lost when uploaded to Later.
Later now grabs the text/caption from the EXIF data and puts into the Media notes!