Need our own kanban board for our team's processes

Our team currently coordinates everything in group chats and dozens of spreadsheets, and this can no longer handle the workload. Messages get lost, it's unclear who is responsible for what, and deadlines are missed simply because there is no single place to see the real status of work. We are looking for a developer to build a full-featured task tracker and project board that works the way we actually do.

The foundation is a kanban board with columns that we can rename and rearrange, and cards that are dragged between them as work progresses. Each task should have an assignee, deadline, priority, tags, description and comment thread, plus checklists or subtasks for small steps. On top of this we need a timeline or Gantt chart view to see how tasks fit across weeks, and team member roles: admin, employee and guest should have different permissions. We want separate boards for each project, filters and search across cards, and notifications via email and in-system when a task is assigned or a deadline is approaching.

Propose a clean responsive interface for desktop and tablet and a thoughtful data model. Show examples of similar boards and provide an estimate with breakdown by stages.