The basic etrex is seriously lacking in memory capacity and in a proprietary data cable you'll have to buy extra.
Do yourself a favor and at least get a Legend (HCx is the best one, but any model with an H will be good enough).
When using MN DNR Garmin to load shapefiles onto your GPS, you will need to keep in mind a few things:
1. the GPS has a track point limit. If the file has more points than the limit, you will lose data and you have no control of it at that point. You will have to simplify the file to fewer points in a line first.
2. Garmin GPSes cannot handle polyline features well. You take one file that contains a network of intersecting lines and attempt to load it onto the GPS, and the GPS will break it up into many, many separate files that will be practically impossible to work with. To load that sort of feature, you have to turn it into a transparent .img file that can load as a map in Garmin Mapsource that can be transferred onto the GPS as a basemap. More steps, but involves free software. You can read tutorials on it at www.gpsfiledepot.com
3. The Garmin GPS cannot interpret a polygon correctly. Even if all you want to do is load a single rectangle, the GPS will interpret it either as a line or a series of waypoints. You will not be able to assign any sort of area symbology to it by just loading a shapefile through MN DNR Garmin. You will have to use the method I mentioned in 2 in order to turn that polygon into a transparent .img file for use as a basemap.
4. the easiest way for any Garmin GPS to handle any sort of GIS data would be to set it up as a Garmin Custom Map in a tiled .kmz that could be loaded onto the newer Garmins (Dakota, Oregon, Colorado, 62, 78). At that point, your only limit is the number of map tiles, but you can layer as many files as you like.