Leave the panel alone till after you get your instrument license. Installing a GPS now will increase the complexity of instrument training several times over. You will have to learn how to operate the new equipment at a very high level for the checkride. While training, simpler is better.
ADS-B out compliance is NOT mandatory for everyone! It depends on the airspace you operate intend to operate. Of you decide you need it you will need an approved GPS source, but the source DOES NOT have to be a GPS navigation system.
There are ADS-B out solutions that have a GPS built in to provide the position source, and these devices are cheaper to buy and install, but they don't add any navigation capability to you aircraft.
The downside to ADS-B compliance besides the cost is the fact that it becomes a no-go item if it breaks. Per the regs, if ADS-B is installed, it must be on at ALL times, even on the ground and in airspace where it is not required.