AE first declaration questions

Hi, it’s time for my first déclaration de chiffre d’affaires and I have some questions I can’t find answers to.

1. All my clients pay in US dollars. I assume it’s okay to use the current exchange rate is to convert to Euros?

2. What category should I declare my earnings in? My options are:
- Chiffre d’affaires des prestations de services commerciales ou artisanales
- Chiffre d’affaires des autres prestations de services
I am a virtual assistant and I provide help with photo retouching for my clients. 100% of the money I’m declaring this time is from those activities (no merchandise sales or other activities). I’m guessing it’s the first option, and the other is if you do some gardening on the side or something like that. Is that correct?

3. Does a tax rate of 23.70% seem right? I watched one of your older videos saying you should always check the rates they apply are correct, but I can’t follow the steps you use to do this (I never received the documents you use in the video, and I don’t know where else to look).

4. When I fill this in online, a red notice comes up at the top of the page saying, “Vous avez opté pour le versement libératoire de l’impôt sur le revenu.” Can you explain what this means please? Does it mean that I’m going to get another tax bill at the end of the year? I thought I had selected to pay my taxes as I go and to NOT have a bill at the end.
If there is going to be another bill at the end, how much should I be setting aside for that?

Thank you!