Filling in URSSAF’s declaration de chiffre d’affaires

I am a freelance software engineer and I moved to France in September. I work remotely from home, part-time, for clients in the UK and the US. They pay me in sterling into a UK bank account. I send them bills electronically based on hours worked or on a fixed-rate charge for a deliverable work piece. I am not going to force my clients to pay into my French Bank account as they already have the accounts set up and it will inconvenience them unnecessarily: I chose to move to France, they did not ask for that change. Looking at my URSSAF turnover declaration I am completely baffled as to how to classify my turnover. I have the following boxes :-

“Code de gestion”  “Activite”
054                 VENTES DE MARCHANDISES ACCRE
510                 EMPOT ACTIVITES DE VENTE
055                 PRESTATIONS DE SERVICES COMMERCIALES OU ARTISANALES ACCRE
520                 IMPOT PRESTATIONS DE SERVICE COMMERCIALES OU ARTISANALES
573                 IMPOT PRESTATIONS DE SERVICE NON COMMERCIALES
576                 FORMATION PROF. OBLIGATOIRE

I don’t sell any merchandise, so the first two are probably out? I am guessing that the next two don’t apply to me as I am not classed as an ‘artisan’ ? I am guessing that code 573 is where my turnover is classified but I am not sure why it is described as ‘non-commercial’ ? and I have no idea what the last item ‘code 576’ is for… I have requested a meeting with them and I am still waiting. Also, do you know what exchange rate I should use to convert my sterling turnover to euros for tax purposes?

Thank you in advance for your help.