Because of the 60Da's modification to increase IR sensitivity for astrophotography, if you plan on using the camera for regular visible-light photography, you probably should get an IR cut filter, otherwise you may experience color shifts when the sensor gathers both visible and non-visible light together (magenta cast with synthetic fabrics, and foliage greens being off are common issues with full-spectrum cameras used without a UV/IR cut filter).

You don't want to get what most people think of as an IR filter (like the Hoya R72). That is an IR-pass filter which blocks visible light and only lets IR through--you're trying to do the opposite: block the IR/UV light. Most IR cut filters will also cut UV, because some cameras don't have IR/UV filters over the sensor (e.g., the Leica M8).

Since UV/IR cut filters aren't cheap, you can get one filter that's the largest size you'll need and then "adapt" it to your other lenses with step-up rings. What size you'll need depends on the lenses you'll be using.