First, no you do0n't NEED an Archon. THe court can be taken as a seperate HQ choice in its own right, but it you also take an Archon then the Court does not count as one of your HQ choices.
Whats important to note in regards to your second question is that the Court do NOT have to form a unit with the Archon. They are a seperate unit the Archon can CHOOSE to join if he so wishes, but does not have to. As such the Archon can join any unit he desires. The Court are not Independent Characters, so can;t join other units.