To be ADSB compliant your GPS needs to have FD&E, not just FD. In the Garmin world the 430/530 are only TSO129, so don't have FD&E. To upgrade to the W variety needs a new processor board and a new GPS receiver board. As a bonus you also get terrain.
You can have the GPS as primary nav and no alternate if you have 2 TSO129 units. If you have a single TSO145/146a GPS it can be primary nav and no alternate.