I select the area, like part of a floor, save it ,but it will save the whole building not just the part I selected.
Are you sure? Does the blueprint really contain the whole building? Please keep in mind that the preview in the journal is just a screenshot showing everything you saw when you created the blueprint, so the whole building may be visible on it, but the blueprint should still just contain the selected part.
When I use my window key to get out of the game to look at something, click on desktop it goes back into game.
When there are issues when alt-tabbing to desktop, and you're running the game in fullscreen mode, I'd recommend to disable fullscreen mode, adapt the ingame resolution to your desktop resolution and check the "Undecorated" box in the settings, that provides an alternative fullscreen mode with less problems 
Still having the same issues, it will completely freeze (unable to do anything, trees stop blowing in the wind, everything stops), unless you're standing still.
Well, when the game freezes completely, it's definitely a clientside issue, not related to the server at all. Please try this: Open console ingame (by pressing ` or ~), type "report" (without quot. marks), then have a look for a file called "report" (followed by a number) in your game directory (Steamversion: Rightclick on rw in steam -> properties -> local files -> browse local files). Please create a new separate topic here in the forum (in this section), and post this file content there 