Great Ocean Road

I'm looking at driving GOR (and a little further) in early January. I have up to 7 nights to play with and seeking advice/tips and must sees/do's (including food!).

So far I'm thinking of starting in Melbourne and staying one night in Apollo Bay > Port Campbell > Portland > then 2 nights at Beach Port before heading back to Melbourne. These locations have mostly been picked due to where accomodation is available but intend on stopping in at all the towns along the way.

Would drawing it out to 7 nights be too long? What other places would be worth staying at/should I spend more than one night in any of the first 3 places?

From what I gather booking accomodation in advance will be required and there's limited freedom camping - is this correct?

Another option could be starting in Melbourne then going right through to Adelaide.
I'm interested in mostly water-based things, cruisey beach vibes and good food, but open to some inland stuff if it's highly recommended. Thanks in advance :)