How do I remove the adhesive from those glow in the dark stars from the ceiling?

Hi all, I have been reading up on estimates for painting houses etc here, and still need some help. I am 'thinking' about going out on my own, have 12 years of 'constrution' experience, and can not figure this estimating for jobs out? So I came up with this. When pricing a job, could we say for example, a 10 x 12 room= 120 sq ft,say 3-4 hours to paint and cutting only, no fixing or primers, and say $50/hour cdn= labour and materials. Materials being 1 gallon paint-$50 (good paint) not the cheap 'painters pro' stuff--roller, brush, drop cloth= $10 give or take. Soooo--$200 for the job and $60 for materials= $140 for you, if you do the work. Pay a 'worker/helper' say $15/hour= $60 buy hi/herself, and you get $80 for doing not much. Am I close on this? Any help would be great all, I am seriously considering a move towards being my own 'boss':)