Just make sure that the habits you inculcate as a BA are sound and productive. In my personal view, it seems each consultant's style/personality (i.e. the style of slides, the writing, the analysis) seem to really form during your time as a junior, so unless you don't know want to go through a hard time as you go up the ladder, buckle up and embrace the suck.

In terms of content, one should always be able to fill out, as a general rule of thumb, around 1~3 slides based on a 1-hour interview with an expert. In order to do that, you must have already have a good understanding of the storyline of the project, and the framework with which you will be approaching the work module you are working on. You do not go into an interview without having a framework to work with, and you must be able to filter out any information that does not fit well with the framework throughout the interview.