placing text accurately kind of sucks in solidworks, but if you want to have it centered you need to draw a line or curve for it to follow. Then you can use dimensions like usual to place it/move it around. if you are going to place it based on the left side, no real need for a curve/line to follow
for your sketch, you need a plane, this can be a flat surface of the part, or you need to create a new plane using the reference geometry tools