Wow, big ask. First I would suggest you contact the Fijian government, their tourism board, foreign investments board, stuff like that, see if they can line you up with the people who know about Fijian boat I g matters, there must be a consulate in London surely, if not, this inter web thingie would probably help.
I would suggest a coastguard boating course would be essential, again, find out from Fiji what if any qualifications the would require to run a charter operation there.
If you can, find a job working on and servicing outboard motors, I would assume you would be looking at running smaller, outboard powered, boats. Doing your own servicing and troubleshooting in the islands would be a massive advantage.
And I would suggest you go somewhere moderately cheap, like the Caribbean, to do a stint as a deckhand on a charter boat there if you can, to learn the skills needed in tropical fishing....rigging lyres, baits, gear, servicing reels, stuff like that
. If you are coming from a background with no experience at all of this sort of thing, you do have a fair bit to learn, luckily though it is fairly easy to pick up the essentials and you can quickly build up some experience as well.
The harder part will be learning to safely operate a boat with customers aboard...book learning here is not as much help as being able to read the sea, deciding when rough is too rough, spot changes in weather or currents, stuff like that.
It'd be a helluva life, it is just rather involved is all, and is I suspect more of a lifestyle choice than a lucrative career choice 😊
Good luck pal.

Thank you for your response, very informative and has provided me with the necessary information to start making this a reality. This is something that I want so badly and I suppose as I approach 30 that Im done with procrastinating now. I want a more chilled way of life. where meeting new people everyday is part of my profession. simplicity is what I want lol. 

mozz wrote: Ever thought of the super yacht industry? great money lots of travel and with a bit of experience you could look for a Fiji based boat and get paid to do all the things you have listed without having to worry about the immigration BS to begin with.

Lol, I don't think you will find operating a tourism charter boat business in the islands a particularly chilled and laid back existence....the more chilled and laid back the locals are, the less you can be, trying to crack the whip to get supplies and services delivered on time and in a hurry, he'll, even getting staff to show up for work on the right day can be an ask....Island Time is something that will seriously cripple your business, if you blow a motor on a Wednesday, and the mechanics tell you they'll get to it on maybe Monday.....you know, island time.
That is why you can always find the expats in the nearest bar....the place drives you to drink!