you can use custom CSS inside the style attribute (in your case it would be: font-size:12px;) if you change the style of the label it should be sufficient. If you would like to style more than just one label or table or form then you can define a style class in your theme package and link it to the relevant item (ie form) via the class attribute.
Yes this is possible. The easiest way would be to select the label and go to the Style property (under Appearance) and select a different Size in the Font tab. You could also set this style on the entire table if you need the size to apply to everything inside the table in the dataview.
As Karol already said, this can be accomplished using the Style property which allows you to apply a style using CSS. Where you should enter this style depends on where you want the style to apply. You can do it on the label if that's the only place you want the smaller font to apply. You can do it for the entire table if you want all fonts inside to be smaller.As the name Cascading Style Sheets (CSS) already suggest, the style will be cascaded.