A Task has a start date and represents a job or work to be done in time. Dependencies are the 'movers' of tasks. This is what lends itself to the idea of Phase-Based Scheduling. A dependency connects tasks to each other, so when one moves, the ones that are dependent upon that task can also move in time on the schedule. It is the if/then function between tasks.

No. The number of dependencies a project has should be a by-product of how many 'things' or elements can cause a task to move. While there may be a human manageable limit on this, the system imposes no hard limit.

Of course not. If you have a schedule that has tasks independent of each other, then you can easily use Foresource in the absence of dependencies to manage your schedule. This would include Foresources powerful Gantt chart and related features.