90x45 blocks. That's the smallest a football pitch has to be but you can make it up to 120x90 blocks but might not be good if you're playing on survival or on a time limit.
I like the effect sharpies give, they put alot more ink on the paper than most do, perhaps too much, but they are meant for permanent. Sharpies are great for drawing, but as other have said, don't bother with coloured ones, they are overpriced and give the same effect as any other fibre tip.