The Minor Victory condition for the Venedians (also shared with the other two factions in the Slavic Nations DLC) is the construction of a special building - the Totem of the Wolf.
The three requirements of which are the following;
1. State religion is shared by 70% of subjects
2. Control of a Timber resource and an Iron resource
3. Building researched on the technology tree.
The Gem resource in the desolate port province near the Venedian is a godsend for trade agreements with non-horde powers. Making friends and getting rich is very easy as long as you can maintain control of it and keep it from being besieged.
The best location to set up for Iron and Timber, in my opinion at any rate, is the Straits of Gibraltar in the South West corner of the map because of the high fertility of the region even in the late game. The Mediterranean islands are nearby - defensible and fertile. There is also a Gem resource in North Africa and a Gold in northern Iberia.
Britain is also a candidate, closer at hand, but hardly prime real estate where fertility is concerned.
Alternatively, you can expand just south-west or south from your starting position. However the presence of the Huns, and a great many powers who will inevitably resent and hate the Huns, means that you will gain nasty enemies which will inevitably divert you from ensuring the proper piety of you holdings and the overland distance will more or less ensure you have a lot of territory to covert.