You'll get lots of advice here, and some of it will conflict, so eventually you'll have to make your own decisions on what to get, what to install, or even whether to install. Here's what I've done, which I'm very happy with.
I have a 1963 P172D, with a 180hp Avcon conversion, which is my "forever" airplane, at my age. I've had it for a little more than 12 years. I've owned in partnership 3 other airplanes; this is all mine.
I do light IFR in it, in addition to lots of VFR flights, including to back country locations and over the mountains. So although I don't really need the latest and greatest avionics, it is pretty well equipped, and it all works well. Over the time I've owned it, I've had all of these installed:
>Garmin 430W, with full US nav coverage kept current; I have terrain/obstacle data updated about every 2 years
>Narco navcom
>King ADF
>PS Engineering audio panel/intercom
>King KT74 transponder (talks to the 430W, provides ADS-B Out)
Also newly installed, I have a Sandia Quattro which replaces the AI. It is electric and has a built-in backup battery, so that if ship's power bellies up, it's good for 1-2 hours. Only my DG is vacuum driven. If I were to lose the vacuum pump, I can maintain heading with the excellent SIRS compass, which I had installed a few years ago--much better than the OEM Airpath compass.
For weather and ADS-B In, I have a Stratus 2 tied to an iPad Mini mounted on the yoke. I also use the Mini as an EFB with a Foreflight Pro subscription, which provides all the geo-referenced charts, both VFR and IFR including all the approach plates, for the entire US. After a year of using it, I have opted out of Synthetic Vision, as it doesn't impress me as being all that usable. I also have Foreflight on my iPhone 5s as a backup, including the Horizon app for a second AI, also tied to the Stratus 2, which I stick on the panel.
The Mini has worked flawlessly for the 3 years I've had it. I have other apps on it, so I can use it away from home for surfing the web and emails.
I also have a Garmin 96C handheld, which is an excellent pocket-size portable. It was my first aviation GPS. It's no longer made, but updates are still provided. It's hardly necessary, but handy for checking on distances, etc., and it has a better map than the 430W for VFR use. I have it mounted on the panel.
I get some good natured flack here for my cluttered panel, but here's what it looks like, before the KT74 and Quattro were installed:

Enjoy your new airplane!
Cary