I clerked at at district court, we had an informal meeting, they gave us some handouts, and we were on our own. Well, not really, chances are you will have an experienced clerk somewhere to help you out.
The Federal Judicial Center has some resources on opinion writing--it is on-line and accessible to the public, and there is a video along with written materials on opinion writing that should be available to you when you start. Some material can be ordered at
www.fjc.gov. (I believe they are free, I know they are to law clerks) I would imagine at the CT level, you'd have more guidance. My co-clerk and Judge sat by designation at the CT. I remember the decisions went through a ton of drafts because every chambers wanted to see them.
Not sure what you mean about the search system. We had Chaser, internal and external which allowed us to search other decisions written by clerks/judges in our district.
The best resource is to read lots and lots of opinions by the judge you are going to clerk for. Most judges have a standard way of writing that is pretty easy to pick up.