Also, would Vikings usually have had wives and children before they sailed out? Put another way, can modern Scandinavians truly be said to be the descendants of Vikings, or did the actual Vikings leave most of their descendants elsewhere?
To break it down really basically, first a lot, and then not much.
Viking activity happens in a series of escalating waves, principally targeting England and France, which can be seen most clearly in the Anglo-Saxon Chronicle. Until the 860s, Viking attacks on England are fast-paced raids. These escalate from single ships to fleets of over 6,000 men, but even these full-scale armies don't stick around long. Depending on the level of resistance they face or how successful their raiding goes, Viking forces "overwinter" - staying in fortified camps during the winter when North Sea storms prevented a safe return but outside of the campaigning season when they were unlikely to be attacked. By the 870s, Viking armies were realising that staying in England, or indeed France, could prove far more lucrative than returning to Scandinavia every winter, and a focus switched to conquest and settlement instead of raiding, culminating in the settlement of the Danelaw and the "5 Boroughs" of the East Midlands until the early-mid 10th Century.
Ryan Lavelle's The Danes In Wessex should provide you with some interesting details.