Questions on BASIC vs Geometry

Hi all thanks for your help. I am new to UE4 and I hv few questions that I find it difficult to answer even I have browsed a lot on internet. Let me explain with an example.

I would like to build a room/house, then I start making the walls, floor etc by using geometry because I can alter the UV of the surface material and apply different materials on different sides. Then the first problem is here: I cannot use the paint mode on this brush type object. (For example I want to paint some rust/dirt on the wall wherever I want, what is the most suitable procedure?)

The second problem is, may I know what are the common procedures for making a room? My interpretation is: build some basic geometry using UE4 (like the walls, floor…), build models (like furnitures) using other modelling softwares like MAYA and import to UE4, create/apply materials using UE4 (is it? I found it much easier to make it in MAYA, but others like the normal map cannot be done by MAYA right?), then the lighting, animation, etc.

Last but not least, I am really new to all of it, including UE4, MAYA, basic of materials… any videos recommended??

Thank you so much for all of these…