Energy does not accumulate. It is a constant, but energy usage is also constant. For example, if you have 100 energy, and your buildings require 100 energy, then you're ok.
Your energy will not go negative. You cannot build a new level of mines if you do not have enough energy. It will say under the building, "Not enough energy." So then you have to upgrade your solar panels first.
Yes, you have new buildings for every planet. However, you do not need to build every building on every planet. For example, you can have just one Science Facility and do all your research from that planet. The same goes for the Trade Center.
When you are on vacation, your mines do not produce. When you return from vacation, you must visit the government page for each planet to restart production.
The resource chart is confusing and doesn't show everything, so I don't use it for anything.