If you intend to fly non-precision or precision GPS approaches, you really do need an IFR GPS. This article explains the options available and the legal issues associated with using the latest in-cockpit GPS technology for IFR navigation; by Stein Bruch.
When you build your own airplane, you get to design the cockpit you’ve always wanted, from the ground up. But facing that blank slate can be challenging and calls for a thoughtful approach.