Updated font sizes and weights for labels, input instructions and input errors.
See #2 (comment) for images.
Labels
font size: 16 px (1 rem)
weight: medium
line height: 20 px*
distance from input border to label: 8 px*
Input instruction
font size: 14 px (.875 rem)
weight: regular
line height: 20 px*
distance from input border to instruction: 8 px*
Input error text
font size: 14 px (.875)
weight: regular
line height: 20*
distance from input border to error text: 8 px*
*Note that 8 pixles and line height 20 refers to actual pixels in design and not margin-bottom: 8 pixels and line height in browser, due to line height affecting actual space between input and text.