For internet-based information on the fields you mention, you could do a lot worse than to take a look at
www.nav2000.com. This little gem is a French-run site that provides all sorts of useful information on pretty-much every French airfield, and a few foreign ones too. Probably not enough to complete your flight planning, but certainly good enough to give you a flavour of the places.
So far as specifics are concerned, I have been to all of the fields you mentioned, and with the exception of the desire to get them into your logbook, in some instances at least, you may find them disappointing.
If we take
Berck as an example, it is effectively the private home of a flying club that specialises in BBQs fly-outs and doing the odd "Bapteme de l'Air". The club is close-knit, and whilst you will be warmly greeted, there will be a degree of surprise to see you. Fuel is often not available for visiting aircraft (since it is administrated by the club) and facilities for met and flight-planning will be basic.
Berck is not really in the town of Berck-sur-Mer, although it is not a long walk to the seafront. It is also next-door to the massive Bagatelle, theme-park, not a bad run if you have kiddies, but definitely quicker to land at Le Touquet and take a taxi.
Turning to
Eu/Mers-le-Treport, this airport is of restricted use, and is only available to aircraft based there, and those based at certain surrounding airfields. Whilst you could obtain permission to land, there is little to do there when you arrive, so few bother unless they have a particular reason for landing there.
Amiens is a nice airport with a lovely little terminal building, stuck some way out of town. Make sure you bring a taxi number and a mobile phone with you to avoid being marooned at the airport with nothing to do.
Albert/Bray is a very friendly little field with a nice hard runway and a friendly aeroclub. There are also some nice restaurants in the neighbouring villages.
St. Omer is another friendly one with an aeroclub that actively encourages visiting aircraft. It is also a little closer to town, and you can readily walk to the town centre. Worth remembering that the grass runway is only available to the residents.
Contact me directly if you want more specific information.