With the motion sensors can I legally have them turn on when someone is close?

Height, weight and other obviously visible statistics should not pose a privacy issue. A person might have a reasonable expectation of privacy for some things, however. For example, the heat-vision mode of the short-lived Sony video cameras from the 90s that would allow you to see a naked outline of a person from that person's heat map. Privacy issue. Weight and height? Not really you can reasonably guess at those things just from seeing someone in public. Likewise, a motion sensor to detect when someone is present is fine. Sounds like you have a neat product on the hoof. Go for it! Take care.

If you are planning to place this somewhere, you will need to follow laws such as laws about advertising, signage, lighting, publicity, etc. In most locations, lighted advertising is strictly controlled and placed. You can and you should, of course, get a method patent on this asap and develop it all you want. Then, when you want to use this or a similar method or product, you can worry about the usage and the laws regarding it. Contact a lawyer.