Sure,
1: The initial download was pretty small ~10GB. But with the models, lora(s), extensions, ect. I'm up to ~60GB.
2: The guide at the top was pretty easy to follow. Install the dependencies, then install the UI. Launch and run. There is a bit of a learning curve with all of the options but so far it hasn't been too confusing.
3: That's where the extra models/lora(s) come in. Various models are trained in different styles, poses, actions, ect. The lora files are smaller things, like poses. IE: Cowgirl is it's own lora file that tells the model how to use the prompts you give.
I did. The file paths can get long depending on what you are doing, and IIRC it's just a small registry change.