AlbinSailor-
Take a look at the past few years...
Ronnie Simpson bought a boat, tried to learn everything he could in a very short period of time, and left on a circumnavigation...only to have to abandon ship a short while later. BTW, he never even got the boat, which was 47 years old or so... surveyed after buying it-but could afford to buy HD camera equipment to document his voyage.
Heather Neill bought a boat, spent a long time working on upgrading it to be the ultimate Flicka, but didn't spend any time working on her boat's captain... set off on a circumnavigation... turned back a day later and hasn't been to sea since AFAIK.
Donna Lange was a grandmother when she learned to sail. She worked her way up by day sailing, weekending, coastal cruising, making short passages, then finally doing her solo circumnavigation. She got the boat and herself ready... both are necessary.
No one is saying that you can't do this... just that you would be wise to work your way up to doing so.