There is no need to update the old model. Assuming you're using A1111, if you update the webui to the latest version (git pull in the command prompt) A1111 will natively support SDXL models. Afterwards, you can freely use this model like any other model in your web UI.

very carefully

download the file, open your stable diffusion webUI folder, go to "models\Stable-diffusion" and copy/cut the file you just downloaded into the "Stable-diffusion" folder. fire up WebUI and change the checkpoint to this one.

about $2.50

Have you tried doing natural language yet?

I noticed you need to use related tags and/or redundant prompts, something like:
breast cutout, cleavage, her dress have a hole in the chest area,
Instead of just breast cutout. Or use parentheses like usual, but it's true most of the time it didn't follow the prompt, I guess we need to wait for updates or merges.

Noticed the same, dunno the cause, but I just use lightroom to increase the vibrance.

Try using the standard SDXL vae instead of the one the model provides, this should solve your problems, it did for me anyway.

Just based on how copyright works with SD generated content, there is no need to mention the model you used because no one owns anything.

@k3415353933 I see this differently; the author of the model explicitly prohibited uploading or selling the model on generation platforms and requires credit when using the model. Here is the license that this refers to: CreativeML Open RAIL++-M.

Credit refers to use cases such as merging, or using it in other models in some ways. Selling the model or using it on generation websites is prohibited.