Custom Type with 2 fields: Date and Number

I'm trying to create a custom post type (they'll be children of another type) to enter weights on specific dates…so 2 fields, date and weight . But with the plugin, I must keep the default Title or Editor. How would you go about creating this post type?

I could keep the title as the weight input field, but then how do I enforce it to be a number, such as 100 or 90.5? Or it could be the date, but then I would need it to be a calendar date selector and enforce date format was entered.