The direct answer to your question Enocurage or discourage playing video games to 4+ year old son is discourage and not encourage. The answer to the sub-question What precautions should I take to make it so my son does not become a games addict as he grows would be is no different from beer or coffe - just disallow at young age. Later, matter of opinion, some avoid, others do not see a problem. Not at the age of four, however.
Later buy one really top range, expensive game per year - with good complex plot and perfect graphics, suitable for age, and allow to play only this game. The game will be much less addictive after once played till the end, making the situation possible to control. But not at the age of four, this should be much later.
Real world activities should always be preferred against the virtual reality. Also good Disney movies may tell more about the world than games and may be preferred if there is really a need to keep the child busy in front of the screen.
To get out of your current situation, offer some good Disney movie or really great toy and use the opportunity to take the game console away. If the toy is appropriate for the age, the child must be able to be busy with it also without you.
In the past games were more related to electronics and programming. If you build a home computer with own hands and then program a game on it, probably can play that game till getting green - will not make any harm. However recent hardcore players do not progress into programmers - games they are used to require large team of professionals to be built.
Educational programs, or games with very strong education background, are not considered "video games" as understood in this question. Also using or learning computer in general should be encouraged beyond doubt, as long as this is not about games.