A note here:
Due to the mathematics of space and cost when you're building a Sensor Boat, you should favor Engines over Sensors in early designs. That is, so long as you're restricted to using Interstellar Sensors, always favor having more Engines than IS.
In general, for the early game, the most cost/effective Sensor Boat (using a standard cargo hull with no miniaturization) is a 2 Interstellar Sensor, 3 Hyperdrive+, 2 Environmental Life Support ship. The next one should be replacing the HyperDrive+ with Ion Drives. It's really not very useful to have more than 2 Interstellar Sensors on a ship, due to the way Sensor Radius scales.
Once you have access to SensorArrays, however, the benefit swaps back to them over drives. Personally, I find the 2 Ion Drives, 2 Environmental Support, and 3 Sensor Arrays work very well for the "AWACS" roll of border guards and fleet accompanyment.
Just Remember, you need to keep those Sensors Boats moving. They work best when running racetrack patterns at full speed.
As to Survey Modules, yeah, I'm with Philocrthetes: build them for anomaly collection and raiding. To start, I make medium hulls, just the Survey Module, Shields (to fight pirates and Graveyards), two of one kind of weapon, 2-3 engines, and as much Life Support as I can get. When I eventually have enough tech to build better, I still stick with Medium Hulls, Survey Module, 2-3 Sensor Arrays, 3 engines, 3 Life Supports, and sufficient weapons and defenses to take down first the Heavily Defended anomalies, and then enough to kill starbases. I tend to use them in the same way the Kriegsmarine used the Deutschland-class "pocket battleship" - singletons able to kill lightly defended stuff with ease, and fast enough (and far-seeing enough) to flee or dodge anything that really threatens them.