It doesn't work that way for a number of reasons. First and foremost is that you have to load the game. If you load everything as you come close, then you had better be running a 64-bit operating system because you'll be needing some ram to walk by houses (don't forget every single fast travel location on the map). That's the biggest reason. If you game console then you could kiss Skyrim goodbye.

As for making a truly open world, it is closed for a couple of reasons. The first is stated above, and the second is that it does not benefit anyone to have open homes. It makes wander packages practically impossible, it makes NPCs at risk to disappear or be killed, it makes it harder for you to sneak, etc. Bethesda can't easily tell NPCs where to walk, your game itself will be extremely buggy, and you will be mad because psychic guards will look in the window and see you.

Modded loading times can be a tiny bit longer, most noticeably on game load,.

I don't understand exactly how OBMM and OMOD files use compression for various mods.

Is there a way to reduce the load time for a very heavily modded install by copying the files directly to your Oblivion/Data folder instead of creating and installing OMODs from the .7z archives?

I have the major overhaul mods, plus OBGEv2, ENBSeries shaders, QTP3, Bananasplit's Better Cities, AWLS, HGEC, Supreme Magicka, Enhanced Economy, some survival mods and a number of others, some of which are installed as OMODs and others directly.

The modded loading time takes about 10x - 20x longer than vanilla oblivion, both for loading the game as well as loading savegames.