That looks like a really good platform to work with. What is your reasoning for keeping it light? Are you going to be running flats in it?
18ft long? what is the width? I am currently working with a 1542. I would love to have an 18 that sounds like a pretty good boat. My 15 ft'er has a 25hp merc on it so I would say anything 25hp or more would be an awesome fit, but motors aren't cheap. Keep us posted on your build I am looking forward to seeing what comes out of it. Maybe by keeping it light you can make something super organized?
On my build I have added about 60 lbs for the deck and that is about it so far. I plan to add a trolling motor and nav lights so the only real weight I would have added is the deck. It might work out for the best for me cause that 25hp is pretty heavy and wants to make that nose rise a bit high so I am hoping the extra weight from the deck, gas tank, and battery up front will help level the boat out a bit.