Cape Town -> Auckland by boat.

I am thinking of travelling to Auckland from Cape Town some time in the next few months. I have done it by air and it is a horribly tiring and boring trip!
I have been wondering if it might be an idea to make it more of an adventure and travel by sea, stopping off at interesting points on the way. My vague idea of an itinerary is:
Cape Town -> Morondava -> Zanzibar -> Praslin -> Diego Garcia - > Colombo -> Great Nicobar -> Kuala Lumpur -> Singapore -> Jakarta -> Kupang -> Darwin -> Brisbane -> Sydney -> Auckland
I am not keen on some expensive cruise ship, so I wondered how one could arrange to get berths on commercial boats between these places - or if there are boats that transport people between these destinations.
I also wonder if anybody has a better, more interesting, itinerary.
I think it would take about a month, but I would obviously need to start the planning well in advance. Can anybody give me good pointers to where to get good information about how to set this all up - and about how much it is likely to cost compared to the air fare?

You will find several freighter travel links on the above search result page.
Unfortunately, most of the newer ships no longer have passenger accommodations.

just a naval base (the Chagos Islanders all got shipped out to Mauritius and are currently fighting a compensation claim), so unlikely that anything other than a naval vessel would visit.
I suggest you read/watch the videos of Michael Palin`s Round the World in 80 Days. He had great trouble getting berths on commercial ships even with the clout & resources of the BBC behind him. One ship was only insured to carry a certain number of people, so 2 of the crew were taken off to make room for Palin & his cameraman - I doubt they`d do that for you!