I have created music and movies knowledge sites for use locally in my country (think of Genius and IMDb). Both were built differently (by different people) and do not share anything.
But I am in a dilemma on how to structure the links in a way that wouldn't have a negative impact on branding and SEO. My choices are (examples):
Structure 1: Subdirectories
Stronger domain authority? They'd each have their own homepage, then I'd grab contents from both sites to display on the frontpage. Frontpage clutter?
Structure 2: Subdomains
Same as 1?
Structure 3: Separate sites, Same name
The M in the name can stand for either music or movies (or just media).
Structure 4: Separate sites, Different names
M for music and F for films.
PS: I had chosen the current name because the M might stand for both music and movies (or I could just call it Media).
Things that worry me are: User experience, Niche sites, SEO, Link juice, Branding, Concentrated promotional efforts.