I only have a pour plane at the bottom. So I won't have to knit them do I?Knitting top and bottom together will not show up on DRC. Only one via may be necessary to avoid an error. You will see lots of examples in datasheets.
For example, the small new chips will often have their ground planes knitted to a much large area of copper on the bottom. That is for heat transfer. As for electrical, it's not entirely the more the better, but do be generous.