I assume you have a Day Sailer II (16'9").
I have a 4hp longshaft Johnson on my 1979 DS II, 2-3 hp is usually plenty, over 5hp is really too big unless you want the ability to plane at higher speed (my 4hp pushes my boat to 6.5 knots+, could maybe go faster if I was able to trim the outboard in a bit more and push the stern up a bit)
If that MinnKota is 10# thrust it should be enough....but barely! Usually 1# of thrust for every 100# of boat (including people, and equipment) is recommended, DS II weighs about 700-800# with 3-4 people.
I bought the 4hp to get a clutch (F-N shift) and the built-in fuel tank with option of remote tank, have used the remote tank exclusively since 2006, only problem is the fuel line makes turning the engine around for reverse a bit awkward...... but I really rarely use reverse anyway. Weight for this engine is about 36-38#. A 4-Stroke 3.5hp will weigh about the same and is available with longshaft (Mercury/Tohatsu/Suzuki)