Couple of question about making models the "correct" way and integrating them with Blueprints in UE4

So I played around with Unreal back when it was released a year ago but I never really did much just looked at some tutorials about blueprints and level design, never made anything worthwhile, but now I’ve decided I want to give it a go again and I need some help with a “couple” of things.

Lets say I want to make a scene of a small neighbourhood with a street, a couple of details dotted around and 6 or so houses.
First of all if I want to make a building with full interiors should I split the mesh up into several pieces? If so, should I split each room into one piece? Every wall/floor into one piece? or just have the exterior and interiors as two seperate meshes?
What would be the pros and cons of each method, Is it better to not use massive meshes for textures sake? etc.
If the exteriors and the interiors are seperate should one side just have a square hole for doors and windows and the other piece fill up the walls thickness or should they meet halfway?

If I make the house as one model outside Unreal and split it into a pieces and import them individually, can I group them up and save that group so I can just copy paste the whole house around?
Would that still allow me to individually manipulate each piece of a placed copy?
Can I add further things to the house group, like light switches, windows and doors that all have their own Blueprints with interactions, like turning on the light, breakable glass etc. and still have it working correctly if I copy it around?
Would it be possible to make chains of Blueprints that all depend on eachother, like a power Box on the street that has to be on for the neighbourhood to have a power and then have every individual house have a main power switch that will affect all the light switches in each building?
Can you hook up the standalone power box to each house even if they’re in “groups”?

Sorry for the wall of text and all the questions, any answer is greatly appreciated. (I apologize for any grammatical or spelling mistakes, English is not my primary language.)

You would want to make buildings into pieces, so that parts that aren’t visible can be hidden. If you have simple geometry, then it’s best to try and keep it into as few separate meshes as possible, each actor adds a draw call and you want to keep the draw call count down. For lighting you have to keep in mind that each mesh gets a single lightmap, so if you have a lot of surfaces you might not get enough detail in the lightmaps even at a high resolution, so with walls and floors you may have to split them up into multiple meshes so that they can use more lightmaps.

As for blueprints, you can construct a building using blueprints and then reuse the blueprint kind of like a saved group, and there’s lots of things you can then do in the blueprint besides just constructing the building.