I know there's great tutorials but which is bthe best a-z

[DaveR]

I gave you a link to start with yesterday.

Does Sketchup get confused as a model goes on a long time?

Well, there isn’t much to your model. Certainly nothing that should make it behave strangely. You really do need to learn about using groups and components. All this loose geometry won’t help. Door swings should be components separate from the floor plan. If I were going to create this as a model I would first draw the perimeter and give it some thickness to create the floor. That geometry would be grouped. Then I would add the walls on top of it. Save labels for LayOut. Certainly at this stage…