The 72 is a good engine for this plane, but you missed an important step of being a newbie. A trainer. It is usually not a good thing for a newbie to skip learning on a trainer first. Even with an instructor you could be setting yourself up for a bag full of little parts that use to look like your Pulse.
If you can , hook up with a club and an instructor, fly their trainer if they have one, get some stick time under your belt. Have him preflight your Pulse for you.
Your putting together a really nice plane, but if you never flown before, odds are your first flight is going to be short and costly
If you go with a Saito, go for the 82 same size as the 72. but less weight more power. like Campy said, bigger bang for the buck. The Magnum and the OS 72. will work fine. The Magnum is the heaviest of the three but also the cheapest. Which ever you choose, you`ll still wind up with a nice plane. Good luck.