Is over-lighting a problem or an advantage (as long as the heat is not too intense)?

Also, this is my first plant, that's why I decided to go with one plant (i have a total of two bag seeds, so I didn't want to go blindly at growing two plants). What are the chances that this will be a hemp or male? I am really hoping it comes out a female!!! But I've never done this before, so I don't know what to expect.

Should I start growing my other seed asap? When does the plant "define" itself as a female or male? I know what to look for when sexing, but for example, is a male, a male from birth?

Thanks to all for answer so far.