Decide right away if you are going to use an STB or a CTB. If using a CTB, now is the time to consider if your current CTB makes sense. Here's a hint eighter way. Revit Has 13 Line wieghts, for you to have more at this point may make things more difficult in the future.
Are you going to go AIA? Again you need to consider how what you are doing now will fit into ABS Layer Keys.
Chances are you won't have all the device styles you need or you won't like the out of the box symbology. See my previous post on creating device styles.
Parametric and Block Based parts will have to be created or modified for certain jobs, so you better be able to do it.
Scheduling and Property Set Definitions
Now what did I leave out? Plenty, but here is your start. I'll be adding more based off your feedback. Good luck if you are heading down this road, and don't be affraid to ask for help. Your reseller istanding by.