I would agree with getting a 10" screen. I really like mine. I think it is wise to buy from a company that you think is going to still be around in 10 years or more, the smaller the company the more likely they may go out of business.
As far as going obsolete it is a hard say, but right now there is nothing big on the horizon in the aviation industry. It is not like it was 10-15 years ago where everything was changing. Now the glass panel has matured and we have some really great choices. Transponders with extended squitter for ADSB out and WAAS GPS navigation has become the new standard and should be here to stay for quite awhile. As long as there aren't any big changes in the industry your panel should be great for 10-20 years.
The Garmin 430/530s have been around for 15 years and are becoming obsolete due to spare parts issues. I believe the Dynon D-180 is almost 15 years old too.
Here is my Garmin G3X, the iPad Mini in the center of the panel isn't shown. If the screen was much smaller you really couldn't see all of the 3 things clearly.