I have all three of the things you are considering on my RT198 and the Ultrex will give you the most bang on the waters you fish.
I know you have Lowrance HDS units on your boat but I would recommend getting the iPilot Link version and then at some point in the future getting a small network capable HB Helix unit to get the Link features and the ability to run Lakemaster maps. You don't need to install the transducer, just provide power and plug the Ultrex network cable directly into the Helix.