They have Germany just next door.
Yes, and they did already immigrate en masse.
Title: Percentage of domestic and foreign migrants of the population of Amsterdam 1626-2008
Blue: born in a foreign country Purple: Born in Amsterdam White: Born in other parts of the Netherlands.
The Blue bar consisted in the 17th century for 50-60% of Germans.
But not only the cities received a constant flood of immigrants. There were also seasonal laborers in the countryside, simply because the Dutch countryside offered higher wages than anywhere else.
... I want you to consider the political and cultural problems created by the rapid importation of a large number of foreigners into tight knit urban communities will close access to the linguistic influences of the home country very close by in a nation wide a population the size of 1800s Netherlands. This is not a recipe for internal civility or political stability.
And that is not true for the Welsh, the Scottish, the Irish, the Northerners in England?
It could even benefit from any Continental Blockade if there is a Napoléon to enforce it, using it to take market shares occupied by British production.
The Walloonian coal areas did just that in OTL.
What if they process it in South Africa and then ship it?
Still too expensive, because of the distance and the many risks involved. South Africa is no option. Maybe Sweden, but not in the early stages.
But in general for Netherlands to be the Centre of the Industrial Revolution it need easy access to domestic coal. Netherlands in OTL was a industrial center, but it build on wind and water energy, and that can simply not compete on the scale with coal.
You highly underestimate
peat. Most of the Energy consumption in the Republic came from that source (estimated 13-19 GJ per person per year, an energy use only reached in the 20th century by most European countries). All of the Thermic (used in manufactories like glass, sugarrefining, saltrefining, etc) and also the largest part of the kinetic use by industries. Water was almost not used, because the country is mostly flat. And a Mill had as disadvantage that it needed a high starting investment, and even more important it is not flexible in use. You can't switch production from sawing to wheat without having to rebuild the mill entirely.
So at very least Netherlands need the full provinces of modern Dutch and Belgian Limburg
The Coal is too deep in the ground there for the initial phase. Wallonia is needed.
If you want an industrial revolution to happen in the Low Countries, I think it might be best if the political center stays in Antwerp. It is closer to the coal and iron deposits and had a long commercial history. Having Amsterdam as the capital incentivizes the Dutch to be a colonial power, but not an industrial one.
I think you have an important point here, although i don't see your solution as the solution. I think it is important that Elites from the Coal areas are well represented and integrated in the government, as they will most likely be the real entrepreneurs (I do wonder though, if that was also the case in England. Can anybody overrule me here?) This is hard in the Republic. They treated the southern catholic parts as conquered areas until the end.