Personally, I would try one character illustrating different concepts in many images. Then for the images which sell well, you can later use the same scenes/props and keywords for new images with a new character, if you want to.

And buyers who use your character to illustrate a business concept (e.g. saving money, worrying about high interest rates, hiring a new employee...) on a website will look at your portfolio and use the same character to illustrate other concepts also.

This is the way Scott Maxwell made a lot of money with his 'gold guy' character.