About auto-entrepreneur

I’m not sure you’ve been notified about my previous questions since it’s almost a week and you haven’t answered it, so I’m rewriting it again here since I urgently need the information.

So, I’ve finished registering my auto-entrepreneur through http://www.autoentrepreneur.urssaf.fr. My questions:

1) I read on another website that, I quote, “you can start billing as soon as you submit the form! Then just mention “SIRET being awarded” on your invoices and quotes. Even if you have not yet received the letter, your SIRET may already be assigned: to find out, visit the Infogreffe website and type your name in the search bar.”
Is this true?

UPDATE: I check the website and found my SIRET/SIREN there but haven’t officially received the letter. Can I start working now?

2) I was thinking of hiring international interns to do some research for my side-project, and I know some colleges outsides France allowing unpaid internships (even make it mandatory). Is it possible for my auto-entrepreneur company?

3) I read that you’ve recommending N26 for the freelancer’s bank account. If I’m already using PayPal and have my personal French bank account, do I still need to open another bank account specifically for my business? Considering my application for an entrepreneur visa later and assuming my income will pass 10k.

4) I’m going to promote the business using a brand (not my name), so website, social media account, everything with that brand, but of course for invoice and legal document it will be in my name. What’s the best time for registering that brand?

I am looking forward to your reply.
Thanks!