You need demo, existing and new layers (I use .d, .e, .n extensions) for construction elements, demo and new layers for annotations/dimensions, and demo (d+e) and new (e+n) layer combinations for views/drawings.
Running the 'Intersections in Layer Combinations' Add-On will give you a good starting point for the intersections. It goes over each layer combination and gives '1' priority to visible layers, '2' to invisible, so that you will never have visible walls intersecting with invisible walls or beams.
You may want to do further tweaking of the combo for subtleties like visible walls that you don't want to intersect, like perhaps existing exterior and new interior, but the add-on does most of the job at the click of a button and a small wait. Eliminating the further tweaking or reducing it to the absolute minimum is a good idea if you suspect that you will want to run the same file through the add-on again in the future, such as if you are still creating layers.
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