Instagram captions run long with the hook in the first line, because only that line shows before 'more'. LinkedIn gets a more measured opening, and meta descriptions are kept inside the 160 characters Google shows.
Does it suggest hashtags?
Yes, and fewer than you might expect. A short set of specific tags reaches more people than thirty broad ones, which now reads as spam to most feeds.
Can I use the same caption everywhere?
You can, and it will underperform on at least two platforms. Each has a different first-line budget and a different tone; generate per platform.