Garmin 705

I'll write this assuming you know nothing about using the Edge 705.

1. City Navigator Europe is very good in my opinion, others may argue differently.

2. Personally I don't think other maps are necessary. Reading maps whilst riding is not the easiest to do at speed. Realistically a quick glance wont give you much help. What maps are good for are navigating planned routes (gives turn by turn directions). A quick glance at a screen shot of a turn indicator really helps. Instruction on plotting and setting up a course/route below.

3. Not really worth freeing up space. A 16gb sd card works in a 705, you wont need all that space and they are cheap now.

4. Yes, back up the Maps. usually the file is called gmapsupp.

If you can get Garmin Mapsource (not sure its still available) you can load the Europe Map to it then individually select areas, ie countries to copy to your sd card.

To navigate a course:

Plot a route on the likes of free websites like : http://bikeroutetoaster.com/BRTWebUI or http://ridewithgps.com/ and save the *.gpx file ride to your desktop.
This will create a course which will give you turn by turn directions. This will give you an audible beep to tell you of a turning, then a screen shot including a section of the junction, an intended direction arrow and the name of the road you are joining will appear.

I find ridewithgps the best/easiest plotting website, yes you have to signup, but it is free.

Just click a start point on the map and then click roads until you get to where you want to be, simple.
Download the course *.gpx file to your desktop.
copy or move the course file you downloaded to your desktop as a *.gpx, to your sd card GPX Folder.

Change the settings in your Garmin

Do this first and only once;
Press Menu>Settings>Routing then make these settings
Calculate Routes=Bicycle,
Guidance Method=Prompted,
Recalculate=Off

Then each time you want to use any GPX file, follow these steps:

Press Menu
Select Where to?
Select Saved courses
Select the course you want to follow
Select Navigate and wait a bit for it to plot the course
Press Start when you're ready to ride

Although its for the Edge 800,http://www.scarletfire.co.uk/foolproof-course-navigation-on-the-garmin-edge-800/ gives you an idea of the screens and options to set up courses.

Hope that helps.

Garmin BaseCamp is the replacement for MapSource. It's a free download from the Garmin website.

I'm guessing that the 705 accepts raster maps like Garmin Discoverer - a full Ordnance Survey Landranger 1:50k map. The unit can calculate and plot/guide routes using City Navigator, but displsy the OS map. It's a useful feature.