Pick the handle before you need it
Use the same handle everywhere if you possibly can. It is worth compromising on the exact wording to get consistency — someone who finds you on one network should be able to guess your handle on another.
Check availability across every network before you commit to any of them. Changing later costs you every link anyone has ever shared.
The bio does one job
It answers 'what is this account for' to someone who has just watched one post and is deciding whether to follow. That is the only job. Not your life story, not a list of adjectives.
Concretely: what you make or do, who it is for, and one reason to stay. Three short lines beats a paragraph.
Business accounts, where it matters
Instagram needs a Business or Creator account before any tool can publish to it — this is a platform rule, not a limitation of your scheduler, and it is the single most common reason a first connection fails.
Facebook publishing happens as a Page, not as a person. YouTube needs a channel, which is not automatically created with a Google account. Set these up before you start rather than mid-launch.