Henrik, to keep the map download as small as possible, select only a few zoom levels, and keep the route download to 1 tile wide. You can get a very long route in a small download if you do it intelligently. If you have a long stretch on interstate, don't download high zoom levels (low zoom numbers) because you don't usually need a lot of detail for interstate driving. Get more detailed maps for your destination area, and any planned stops. I usually compromise, by getting a zoom level of 4 or 5 for the route, and no other levels. This gives a pretty detailed view, and doesn't take up a lot of room on my card. You might get a zoom level of 12 or 15 or so for the entire route, just so you can see the whole thing on one page, and that won't take up too much room. Do not get every zoom level for everywhere, or you're looking at gigabytes of storage, and you will likely never use much of it anyway.

For the start and end points, you can use an address or lat/lon, or both. I generally just put in the address. MM saves addresses, so if I want to start from home that's already in the list to be picked, and you can also choose to use your current position as the start point. If you want, you can start another route using the end point, or easily download the reverse route. I suggest installing MM and reading the help file, which is excellent and very complete. If you decide you don't like it you can always uninstall it.