1. Yes, you have to use bodyshop. You don't have to create them in bodyshop, you can use CAS but then you'd need to use simpe to extract them into bodyshop so cut out the middle man and create them in bodyshop! Yes you can use all custom content however when uploading them to a site to share you must give links and credit for all CC used and you should not upload them with pay content.
2. you can upload sims here, or mts2 or most places where they have a forum for community downloads
3. see
here for instructions on how to upload to this site.
Are there any other specific tutorials that you need??
good luck and I look forward to seeing what you have to share
