Yup, schelpenpaden are a national memory. Less ideal for soggy conditions and high traffic as the shells will simply sink into the ground under the weight of travellers.
I'm of a mind with the previous posters: Small outposts, not much more than a village police station or lighthouse at crossroads and important locations: a lookout tower, and a small office/barracks for one or two people. At more important locations: small barracks, enough to house a single squad of infantry/cavalry and a housekeeper.
And yes, "armenkolonies" or "veenkolonies" (aka paupers colonies) as well, as "terraforming" locations, similar to how they were used in the larger Dutch polders.
Knowing the Dutch, there will certainly be the occasional church or wilderness chapel dotting the land as well. Some Christian, but with influence of Doggerland, pagan or paganised ones will also occur.
All cool ideas for Doggerland terrain and/or scenarios: Maybe the wilderness chapel has attracted/angered a local entity and it is determined to defend the chapel, or punish any passerby for it's existence?
A pauper colony is under attack by sea creatures, do you help them, or use the fight as a cover for your raid?
And Dutch magic I assume to be either subtle and deceptive, to give an edge in trade or influence people, or folk magic dialled up to eleven, "wijze wieven" (wise women) who can do unusual, but not particularly flashy stuff. An old spinster in traditional dress that, if accompanying the troops, they always seem to reload faster, or their wounds somehow don't get infected, or the enemies fire is less accurate?
Something to think of as well is that Indonesia was still a colony of the Netherlands. Maybe, confronted with the awakening of magic in the Doggerland, some entrepeneur acquired some specialist support from a land already filled with mysticism, magic and "quiet power"?