These are the five things I ask in the first ten minutes of every migration call. Answer them here and we skip to the useful part: SharePoint or Dataverse, the licence line against your headcount, and the band the build lands in. Rough answers are fine.
Prefer to read first? The decision these answers feed is in moving a SQL Server database into Microsoft 365, the mechanics per source are on the migration hub, and the full 38 points are on the migration checklist.