The parts manager is a really nice addition to the game, as it allows for easier access to parts that are hidden and more awkward to reach, however I have a suggestion.
As you already know, many people miss having the ability to right click on a part and having the ability to see the settings for that individual part. Having the parts manager open up as a large box just takes up too much room on the screen for such a small change you want to make.
What I'd suggest is to still have access to the parts manager via the button at the bottom of the screen. But when right clicking on an individual part, it only brings up a small pop-up menu for that part only, like in KSP1. That way you have the best of both worlds.
Also the close button at the top right corner of the parts manager needs to be larger, it's kinda difficult to click on it and turn the menu off. I've found myself having the just click on the parts manager button at the bottom of the screen instead.