Check out the checklist, then check out afterblast's very good post. I have my certification, I have most of the tools, but ......................... I don't do sealed system work anymore. Why ..... (we've discussed this before) But before I tell you these, If you have no formal training you will find sealed system has many pitfalls to deal with. I went to school for 3 years to learn all this, plus many years of experience. It's not something you want to just go in and wing. Plus you need license and certifications.
First, Time consuming. In time you do a sealed system job, you could do several easier, smaller jobs and make same money or more. Less headache.
Second, if there is a problem, it's not like you have to go back and replace a bad thermostat. Try re-doing a sealed system job gone bad.
Third, Too many tools. Too many items to carry in. Too much work. And how many of these jobs are you gonna get? If your a 1 man company like Me and alot of the guys on this board, believe me it's not worth the time and effort. Plus you lose alot of other jobs because in the end you only have so much time in a week. If you are part of a big company and do warranty work, you may have to have someone doing sealed system. Those are the only guys that do it by me, the Big companies with lots of techs.