Driving abroad isn't too bad. For us it takes about 20-30 mins to get used to the signs and 'feel' of it then it's generally ok. Overtaking is the hardest bit, but the passenger can help a bit. Most of Scandinavia (aside from cities) has less traffic per se so you've plenty of time to map read, sign read, pull over etc. Holland is less so, that's quite urban and busy but you could plan to arrive on a Sunday when roads are quieter to give yourself a day to acclimatise. As well as a Sat Nav I would also recommend a good road map from Amazon/WHSmiths as it can be easier to plan an itinerary and to 'foresee' where you are heading. Use the RAC/AA site to check out rules/regulations- be aware that some are law and other recommended (there are many 'pack's to buy and you may not need everything).
We have camped extensively in Denmark, less so Sweden and we've also done a trip to Holland so can help with areas/sites for those. Language shouldn't be a problem- the written languages are reasonably easy to decode (especially if you've got some German background). Because Dutch and Scandinavian languages are not as internationally spoken as French or German most people are happy to use English. My best efforts in Danish were often replied to in English....
In both Denmark and Holland they are set up for cycling as a way of life- to get to shops etc but I feel the cycling is better in Denmark, as there are a few more touristy and long distance trails.
Denmark has a good mixture of activities- there are beaches (though not your Med sort), lots of history, much of which is free such as Viking burial grounds, outdoor activities, museums, legoland, water parks- whatever you fancy. We found The Netherlands to be a bit more expensive to do things- they often charge per child for museums.
Google is your friend to find places- try terms such as camp grounds, camp places as well as camp sites (the literal translation). Then use google translate if needed for websites, or for sending enquiries.
Holland can be a bit of a pain regarding money- credit cards are not as widely accepted and we had to arrange a bank transfer to do 2 deposits for sites. We used transferwise which was way cheaper than going through the bank.
How would you go about getting there? The ferry to Holland from Harwich worked well for us, but there are now no longer direct sevrices to Denmark. A new company- Regina Line is supposed to be starting in April but I have never used that.
For sites in Denmark, we had an individual fire at Mons Klint but can't recall any others having individual fire, many have communal ones. There are a few camp grounds organisations www.danishcampsites.dk/ and www.dk-camp.dk/?lanGuid=3. Another great thing is that many Danish sites have free kitchen facilities- we just take a box of plates/pans/cutlery and a small gas for those times we fancy a brew at the tent. Saves a lot of space! Our fav places are Skagen, Ebeltoft, Aero, Bornholm, Ribe, Faaborg and of course Copenhagen, is THE best camp site for the capital If you do spend any time in the capital, consider getting a copenhagen card as it covers travel and entrance fees and we loved it here
For The Netherlands, look at the nature camp grounds. We found it harder to find smaller sites as many google searches link to places like Duinrell etc. We loved it www.campingschoonenberg.nl/here and this was a good base for Haarlem, Enkhuizen and Amsterdam, as well as the north Holland touristy places. We also stayed here and whilst it was a lovely site to rest on, there wasn't as many things in the area to do.
HTH but let me know if there's any more info you'd like.