Learn on a small boat... because you'll learn a lot more about sail trim and boat balance on a dinghy than you will on a larger boat
Join a local sailing club or yacht club. Sail as much as you can, and crew on a races, even if they're just 'round the can' type races. The performance tweaking tips you learn racing are important for sailing in heavy and light air in a cruising boat.
Get Dave Seidman's book, The Complete Sailor
. It covers a very wide area of sailing theory, history, techniques, skills, and is well written, easy to read with good, and amusing, illustrations.
Trimarans are not really good liveaboards in some ways.
If you take three boats, a monohull, a catamaran and a trimaran of the same LOA, the catamaran will have the most room and the worst sailing performance, the trimaran will generally have the least room and best sailing performance, and the monohull will have a moderate amount of room, but the most weight carrying capacity.
Trimarans have a smaller cabin and far less stowage than monohulls or catamarans of the same LOA. One reason is the hull form on a trimaran is much longer and narrower than that of a monohull, and has much shallower bilges—limiting both the amount of living space and stowage.
A catamaran has two hulls, usually longer and narrower than a monohull of the same LOA, but has the entire bridgedeck that connects the two hulls, so often has much, much more living room and stowage—however, if you were to load down the catamaran, it would sail like a pig. Many of the big cruising catamarans down in the Caribbean have to motor in light air for this reason.
Monohulls have more stowage and living space than trimarans, but less than the much wider bridgedeck-equipped catamarans. However, a monohull usually has a much greater displacement than a trimaran or catamaran of the same LOA and a greater PPI than either—so you can often load more supplies, equipment and people into a monohull before it negatively impacts the performance, than you could in a trimaran or catamaran.
Start slow... get a boat, learn the boat's personality and quirks, take the boat on progressively longer trips, with exposure to greater varieties of weather and sea conditions. Start off coastal cruising, and then slowly work your way out to short ocean passages, then longer ones... If you're serious, you can get the skills and experience you need to do this in a couple of years. Then set off on your circumnavigation.
Don't announce your circumnavigation to the world like Heather
did. Do it quietly and competently. If you announce it, the amount of pressure on you to start will probably overwhelm you. Most people sail around the world by sailing one-day at a time... and many never intended to circumnavigate... but just wanted to sail.