Basically mate you can go for the rate I the area which you are in or you can go for what ever you teams can do it for as long as you can make some money o it of it.
Start wiv the profit u'd like to earn then work ur trading costs etc out hey presto ur left with your rate....unfortunitly there'll always be people undercutting ya
Linea/meter/sq. It doesnt really matter as they'll all work out the same in the end