A friend who works in Marketing was starting to use video as as a marketing and sales tool. She called me up to ask me about video asset management software, and also "how many videos" she should have. There's no hard and fast rule on how many videos you need. Content is king. If it's not good or does not benefit the viewer in some way, it doesn't make a difference if you have 10 or 1000 videos. One, really good video, that is watched a lot can be a very effective tool in a marketing campaign. If you start with a number in your head of how many videos you "need," you will start making up garbage to fill that number. Remember when you had to write a 20 page book report in high school. Eight pages of it was good, and the rest was fluff and filler. Same deal here!
You are using online video publishing as one tool in a mix of other tools to run a marketing campaign. It is another way to present information, evoke emotion, serve a call to action, and to entertain. Actually, entertainment is one of, if not the most important parts.
Pretend there is a slider between Education and Entertainment:
Education: --|--------------- :Entertainment
More towards the eductaion side is very informative.
Education: ---------------|-- :Entertainment
More towards the entertainment side is not as informative, but keeps more viewers for entertainment/emotional appeal.
There is no rule as to where you should sit on this, but IMHO, it is better to lean more on entertainment, less on information, and do more videos to get out all of your information.
A collection of great examples are the Blendtec videos on Youtube.
All you need to do is watch and you will get what I mean. They are about 99% entertainment, and 1% information... but they have very effectively pounded home the message that they can mess stuff up in a hurry.
Check out: http://www.youtube.com/user/Blendtec
BTW: I highly recomend watching the Chuck Norris one!
And of course, the more videos you produce, the more video asset management systems can help you organize and distribute your content.