Yes to the Tiny Tach. Great tool. Forget the fancy option version. I have tried other tools. Checking a prop needs two things. Tach and GPS.
I believe your engine has a maximum RPM of 5500. This is your target. The Acceptable Full-Throttle Range is 4500-5500RPM. Consult your specific manual to be sure. The engine must run in this range at full throttle. If it can't run fast enough it is being overloaded and may ping and overheat. If it is running too fast, it is being over revved and can tear itself apart if severe. Either condition reduces performance and can destroy the engine...sooner or later. Some of these engines have a range 5200-5800 so I don't mind running them a little on the high side. If you see 56-5700 don't panic. Some models have a rev limiter in the ignition module set at 5800 or 6100. If you hear the engine skipping at full speed, it is likely bouncing off the rev limiter. Now you NEED a prop with more pitch, slow the engine down a little.
Unload the boat completely and trim the boat for maximum speed. Run the boat at wide-open throttle and note the RPM and speed. Your engine should run in the factory specified RPM range...at or near the top of the range. If the engine is over revving you will need to increase pitch to reduce the RPM. If your engine is running too low an RPM then you will need a prop with a lower pitch so it can rev up a little higher. If it is over-revving 'a little' , it might be fine with the boat loaded normally. Careful buying too much pitch. If you are wrong you're stuck with it.
You do this with an empty boat, and aim for the top of the RPM range. That way, as you load the boat with persons/gear, the RPM will drop off but still be in the acceptable range. If you load the boat severely, the RPM may drop below the lower end of your RPM range. Your spare prop should be one size smaller to allow it's use during a heavily loaded day out. Rule of thumb...you can use a prop one size too small. You can never use a prop that's too big. Make purchases carefully.
I like stainless props. They have thinner, stronger, sharper blades. They are more efficient when performance is critical. For every day use, especially in unknown waters, aluminum is a more practical choice. It will give if you hit a solid object. It is repairable at lower cost. The loss of performance, for these engines, is hardly noticeable without a GPS. An aluminum prop is less likely to become the property of the local thief.
Your GPS is nice because you can see small changes in top speed for various conditions. These are flat or choppy seas, with or against the wind, all-important trim angle, and even slight differences in identical props.
I spend lots of time setting up boats with a Tiny Tach and a GPS. It seems though that I always guess wrong on the initial set-up. Your 16ft boat should make pretty good use of the 13pitch standard OMC prop. Some engines are stronger than expected and can use a 15pitch. A 30hp engine set up with a big carb on a good lightweight hull can occasionally make use of the factory 17pitch stainless 'cupped' prop. Condition of your prop is critical. A banged up, distorted prop is useless. Two of my personal boats are Alumacrafts. They work well.