Many people easily speak English, so don’t hesitate for inquiries. The dialect in the south sounds pretty German.
April is in spring season and can have all kind of weather: cold (still freezing at night) to warm (exceptionally about 20°). April is known for windy rainy days so don’t forget your raincoat. And, as many people are biking, they like to be update about rain showers by looking at http://www.buienradar.nl/. More information at http://www.weeronline.nl/.
If you want to know more about the Dutch habits, there are several books available e.g. The Undutchables 6.0, The Holland handbook. Above all you can experience it!
Of course there are a lot of attractive activities to do in the south. And you can also to expand your trip to other European countries. Heerlen and Maastricht have a tourist office where you can go for inquiries or look at their websites: http://www.vvvzuidlimburg.nl/vestigingen/vestiging.aspx?id=24 or http://vvvmaastricht.nl/?lang=1