Hi Kilda, you mention tides. Please note that a motor is a sailing aid not a navigation aid.
Let me explain. Assuming no sensible size motor will push a Wayfarer in to a plane, it’s hull speed is your speed limit. A Wayfarer’s hull speed is approximately 5 knots. That is 5 knots relative to the water that surrounds you, hence it is a sailing aid. Obviously, if you are faced with tidal currents you have a navigation issue if these currents are stronger then your hull speed. In that case you have to plan another route or wait until the tide turns.
My guess is you would need 10 to 15 HP to push a Wayfarer in to a plane but I would not want such a heavy engine on my transom, let alone what the the forces of such a bugger would do to my poor transom. The sensible choice is around 2 HP. Such an engine weighs between 11 and 14 kg. (A 4 HP weighs double that). A 2HP is perfectly capable of getting your Wayfarer up to hull speed, even in a chop. IMHO anything over 2 HP you buy for others (as in towing).
A long shaft is better in a chop but a short shaft is nice to explore shallow waters.Though a short shaft is known to sometimes push air in strong waves, it will still get you home. Shaft length is about personal preference or maybe your sailing area dictates your choice? Oh, one more thing,when tilted up on the transom, a long shaft drags through the water more often then a short tail.
I have a short Honda 2.2 with an automatic clutch but Suzuki has recently introduced a 2.5 HP 4-stroke that has a manual clutch. I would certainly consider that one too. Clutch-less engines would not be high on my list for they keep pushing even at idle. (Swimmers, rudder or propeller damage, docking problems).