Hey Anthony!
Welcome back to the forum. I know where you're coming from w\being a bit apprehensive starting up. One thing you have to remember is that you don't have to take every job thrown your way. Take the ones you're comfortable with at first and advance as the experience comes along. Mix that with practicing on the difficult stones,stains scratches and etches you'll be ready for the on site jobs.
Here's one of the cool things about the NSRA forum (as Jo mentioned)- if you're unsure how to approach the job, post it with pics you'll get a response from the pros.If I'm unfamiliar with a certain surface or stain- whatever, I'll book the job for a later date and get advice here, figure out the procedure and get it done. A little slower than Topshop, Cheesedog or Huligar maybe...
This forum has pulled me out of a few jams just by studying the methods posted. I also keep a notebook with info that might come handy in the future. Print out the poulticing guide. And keep posting!