I'm near Lodeve so we're not too far :)
Signing up an AE regime is probably easier than registering to a Forum ::)))
That's the good news.
Have you been in touch with a network like the BGE and get some (free) counsel ?
I suggest you do this.
They can explain you very easily what statute to adopt and even in the registration.
Its not obligatory to have a separate bank account for your business activity but I would suggest you to do so from the beginning to keep all things clear and separate.
As a writer you will likely fall in the "liberale statute" and If i'm not wrong be taxed 21 something % on your chiffre d'affaire.
As a AE you cannot deduct costs.
If you have further questions, feel free to shoot but I would strongly suggest to look out for a more professional advice.
Cheers - Ivan