They are certainly fascinating and in a league by themselves. If you are going to take one on I recommend allowing at least a year or 18 months minimum to completion. Not budgeting enough time will cause you frustration.
Frustration is something else that comes packed in these kits. Jim is right on when he recommends starting with something smaller with one or two masts. It is fine to build up a few cannons but when there are 74+ in the kit patience can wear thin. Also expect to rig upwards of 500 blocks, even without sails.
A lot of these kits are just like 1:72 aircraft in that they include fit problems, sometimes poor materials (example; lower deck cannon barrels that pin to the hull to represent the whole weapon) inappropriate fittings, out of scale parts (usually rigging thread blocks and sails) etc. The ones you see that look gorgeous were probably kit bashed somewhat.
Not to scare you off, but be prepared for what you will get into. Remember about 80% of these large ship kits never get completed because the buyers were not prepared for the time and patience commitment.
I started with a small sailing dory. I got to make a hull mold, build a lapstrake hull, scratch build metal fittings, rig a mast, make sails, in short everything you will do in a large ship with all of the rewards but without the frustration. If you get through a kit like that (there are many out there) and enjoy it, then by all means work up to the larger vessels.
Two good references that I have mentioned in this forum before are "Historic Ship Models" by Wolfram zu Mondfeld (available in English or German), and "Ship Modelling from Scratch" by Edwin Leaf. A lot of what is in these books can refer to kit builds.
Good luck, I hope I have not scared you too much, I intended a reality check only. Please let us know how you proceed from here.
Bruce