There are different types of Aires - those reserved for motorhomes, often in towns or villages, where you can't stay with a caravan, and those Service Stations, and Picnic stops on the autoroutes, where you can stay overnight free of charge - but most people don't recommend it and no doubt you'll get warnings about this, too.
We usually stay for a first night on an Aire that we know well (Aire de la Baie de Somme), and that we've visited in daylight. We do this because we arrive very late in France out of choice, and it's too late to find a campsite. However, your question suggests you don't know France well - and personally I wouldn't want to sleep over somewhere that I hadn't 'tried and tested'. Some places are quieter than others, some more caravan friendly, and one or two even have hook-up bollards where you can get electricity and water from a coin-operated meter. (Aire des Deux Caps, near Boulogne is one such). On all our other overnight stops except the first night we always find a campsite, getting there mid-afternoon, and then we can explore the town or village, find somewhere nice to shop, and fill up with petrol at the local supermarket (cheaper prices than on the autoroute). Some of these overnight stops have become favourites over the years, and some we've stayed on for the whole of our holiday and gone back to time and again.
You can stay over in municipal campsites - many towns and villages have them, you don't need to book, and usually they are a reasonable price. If you're wanting somewhere to stay overnight on a journey to somewhere else then far nicer to plan your stay around a lovely site en-route - which may become a firm favourite and somewhere you want to go back to.
If you are going to sleep over on an Aire then make sure you're not one of the people who report everything being stolen whilst they were asleep. Make sure you hide all your valuables in one of the many tucked-away places in your van, keep cash in separate amounts in different places, and keep a dummy wallet with a few old cards and some low denomination notes. There are certainly places in our van where valuables could only be accessed if they got us both out of bed, and knew the interior of our van intimately! DON'T leave all your valuables on the table as some people seem to do when they report that their cash, handbags, cameras, passports, wallets, jewellery and car documents were stolen.