I have a 55# Terrova on my 17' Mako ProSkiff and have been pleased with the performance but as SkiffinIdaho points out it all depends on your normal conditions. I fish fresh water lakes in North Texas where there is no tide but usually wind. Under normal conditions if I run at max/10 it will pull my boat at 2.5mph. On a relatively calm day I won't set it on more than 3 and that will be about 1mph.
If I were going to do it again I'd probably opt for the next longer shaft(54" I believe) just because in heavy chop I must drop the motor all the way down to keep the prop completely in the water. I don't know how high your bow is from the water but you might want to think about that.
MinnKota Riptide 55 ST Bowmount Trolling Motor with i-Pilot and brand new never used spare prop and two spare remote batteries. This is a 12 volt model and can easily run all day. Its the most thrust available without moving to a 24 volt.
Here is the exact motor I'm getting rid of for $800. I bought this motor brandy new and sold the boat I mounted it on. The motor has been awesome for me and ipilot (GPS) allows you to set and record courses and of course hit the anchor button and the motor will hold your boat within 5 ft of your spot.
I just looked at a 17 Stratos Flats boat and it looks fairly heavy. I would check with other Stratos owners and see what they are using. I just put an iPilot 55 on my 16.4 skiff but the hull weighs under 400lbs.
As mentioned above, the size TM needed depends on the size and weight of the boat, wind, tide and current. If you plan on fishing inlets with a ripping current for snook or tarpon you might want to go with a 24 V. To keep weight and size down go with Odessey 1200 batteries.