I just completed my
circumnavigation last week. 7 years ago I was about where you are now.
Buy the bigger boat sooner rather than later. It will need some
work before you go, and you need time to do that. It took me 2.5 years, starting with a boat that was a good weekend/coastal boat already. You also want to learn all the systems because unexpected things will break. Paying to have them fixed in foreign
ports inevitably leads to them being fixed wrong. So, make sure you know the boat very well. I helped countless cruisers that had things messed up by incompetent professionals in foreign
ports.
I found the book, The Voyagers Handbook, extremely valuable in selecting a boat and outfitting it and getting ready in general.
https://www.amazon.com/Voyagers-Hand.../dp/0071437657
Plan to join a rally of some kind for your first leg or two. After you get that behind you, I wouldn't bother with them again, but many sailors always cross oceans in a rally. Joining a rally (at least the right one) gives you some confidence that other sailors or officials will look at your boat to make sure it is
seaworthy. It sets a date, and keeps you in a group in case something goes wrong. Not all rallies give that kind of support, but look for one that does.
My first leg was the Pacific Cup, which I selected because of the extensive
inspection and
equipment list. I knew that if I passed, my boat was safe. I would suggest following that list, even if you don't join a rally that has as thorough
equipment list.
https://2022.pacificcup.org/pcer.csv
Set a firm date. This is another plus with a Rally. Without a firm date, people tend to inch toward leaving, but never leave. Once you join a rally and start prepping for it, you are committed and much more likely to leave.
Instead of charting a boat, try to crew for others in an
offshore rally. Chartering a boat has almost nothing in common with cruising. But if you crew on a Rally, you will get the full
experience of crossing an ocean, how to manage the
galley underway, how to provision, what little things you need that you otherwise might not consider etc. Plus, it will be a lot cheaper.
One thing that really surprised me, probably half the circumnavigators I met had a
rigging failure of some kind along the way. Including myself, with brand new
rigging when I left, and others with new rigging. Learn how to do a thorough
inspection, do and inspection before and after each
passage, and know how to replace a
shroud should you need to order a new one made and replace it yourself.