I think, when You select a part (selection of maptiles) of Belgium and the Netherlands from this Topomaps, You get a file of 150-200 MB or >. And Your Dakota is not suitable for Topo Pro/Activerouting maps.
Alternative You can choose a selection of a map from openstreetmap.org. Good quality of data for BeNeLux .
Just go to
Spoiler: Garmin openstreetmap
garmin.openstreetmap.nl
or
Spoiler: Openfietsmap
www.openfietsmap.nl
(Maybe choose Benelux Light version)

There are also instructions on the Internet for making an own map for a Etrex10 (less space, also suitable for Dakota 10) on the Internet, see for an example:
Spoiler: Etrex10maps
https://sites.google.com/site/etrex10maps/
or
Spoiler: Maroufi Etrex10
http://gps.maroufi.net/etrex10map.shtml