1. You can switch to and from State Enterprise as if it was a fully separate category. And as long as your Public Services isn't underwater, it will chug along. You don't need to manage it per se, but you do have a lot of power in determining the direction it should take, and that may be something to keep in mind as you're working out your national objectives. The main example is steel: everyone wants to build steel, but it's seldom really profitable to do so. Here, having 1 State as opposed to 1 Private Enterprise means you can force a steel industry to develop, in accordance with your national aims.
2. One point per project! You may really want to invest in a project's success, though. I would recommend doing that in this system as TWO projects: one which is your main dish, and the other which is a second course, or an aperitif or something. So let's say your first project was "Find a place in cliffs country to build a new hydroelectric dam," your second project attendant to that might be "Build new transformer stations and high-voltage power lines throughout the country as necessary to distribute that power." That will get these projects started and siphon resources from the state and the markets in general as necessary to complete the project, and it may ask you to invest again on the following year (mentioned in the update).
You might think of this as covering your bases, and it's not always necessary to do that if the context doesn't establish a need. There will of course almost always be unforeseen consequences of one kind or another, per the nature of the age and the core themes of the game, but there won't be alien space bats. Well, they won't be bats. (That's a joke, ha ha!)
