The Right Boat
I don''t mean to be critical or amusing but...20 knots of true wind qualifies for Small Craft Warning...which your small craft qualifies for.
I think you would have to research the vessal you are looking at quite a bit to understand how seaworthy it is. More than likely the owner will not let you sea trial it without a contract and even if you put a contract on the boat and sea trial it, there is still no assurance that sea trial will let you discover all the boat''s characteristics in the various types of weather you will sail in.
Going from your Tbird to a big steel schooner would be like going from a motor scooter to a 18 wheeler. A schooner does not really sail at all like a sloop and a steel boat is a big prospect for constant maintenance. I am sure a nice 40 ft schooner could be a good livaboard but I would not think it would give you the thrill of sailing like your T bird does or the speed and pointing ability of a modern designed sloop. It would certainly be the antithesis of a powerboat, even though you would be motoring quite a bit.
I guess I have not understood what your goals, interests and experience are.
Best of luck