Advice sought on seasonal / casual working in France

Good Morning! Can anyone help please…? We live in the UK but have been invited to do a 6 month house-sit near Bergerac from March until September next year and would love to accept the opportunity. The house owners have said there could be some part-time decorating work available on the house for my husband (who has his own decorating company in the UK), while we’re there, and they would like to pay him to carry this out. However, we are unsure on the French law / rules for seasonal / temporary work of this nature. Is there a maximum number of hours he could work / euros he could earn on a casual basis? Would he need to acquire any formal employment ‘status’ to enable this arrangement? If so, which one and how would he go about it? At present we are exploring different areas of France with a view to moving over to settle somewhere, at which point he would apply for his Siret status, but just need some advice on how he can work a little in the interim. Any signposting to appropriate websites or other information would be gratefully received! Thanks, Nicky.