Ahhh... A data standards thread. As I usually say, "The thing about standards is there are so many to choose from..."
I was hired by a county to examine the use of the LGIM and it's okay, but trying to stuff an incrediably broad range of data and data-uses into a one-size fits all model isn't just challenging, it's pretty much next to impossible. Hence my opening quote.
On the other hand, LGIM may be Heaven sent in your case. How data-rich and mature is your organization? Are there established workflows that experienced GIS analysts have used and would like to continue to use? Do you share data with other agencies or obtain data from agencies? If so, what model or standards are used?
It sounds more like your situation could use a standard and since the LGIM is avaialble, why not use it? Consider also that you can use the LGIM as guide rather than a hard-fast model. Use the components that work for you, and disregard those that don't. There are number of ESRI tools that were developed to dovetail into the LGIM, so consider them as well.
As far as migrating your exisiting data into the LGIM or any other model: take your time. Examine your absolute bare bones needs, add what-ever fluff would be nice and then build or use a cross-walk like the Simple Data Loader or the Append tool that map your existing fields to the target feature class.
That should just about do it....