How do I fill in declaration trimestrielle de recettes?

I established my business in France on 7 July 2016. I just received the declaration trimestrielle de recettes (3e trimestre 2016) to be completed by 31 January 2017. Noting the fact sheet that you provided with my business registration, I needed to wait till December 2016. I imagine that means 31 December - end of 4e to return the completed form back.

1. I should wait until after 31 December 2016 to complete this form (even though it states 3e trimestre)
2. Déduction in this case is only credit received from URSSAF, i.e. cette case vous permet de déduire un éventuel credit que vous détenez auprès de l’urssaf au titre de la présente activité? This does not mean equipment purchased, travel expenses, assurance etc during the trimestre that you can deduct from your income?
3. what does changement de regime d’imposition and vous relevez d’un regime réel d’imposition depuis le… mean? Do I need to fill this out?
4. Do I need to provide a cheque (to URSSAF) for the final amount montant a payer along with this form at the same time, or will URSSAF write to me back to confirm and then I pay?
5. I see people talking about paying online with netentreprises.com etc. I Have not found any info on this in my material I have received.
6. I have a second activity (yoga teaching) which is where the bulk of my income is being generated from rather than my first activity (bureau d’etude technique). When we completed the business registration there was not enough space to include the yoga teaching profession. You mentioned, that I should state this second activity in my declaration. Where should I state this exactly?