I would suggest that may be the wrong way to go about starting your data warehouse. Start by identifying a prioritised set of requirements. Do the modelling and data sourcing necessary to support those requirements, then iterate: repeat the process for the next set of priorities.

The requirements and modelling for a data warehouse should be subject-oriented and very specific to your business needs. You won't find any of that in your accounting system which will normally be extremely generic and business-agnostic. You may well find that most or all of your requirements can be supported by a small fraction of the data model in your accounting system - in which case most of the time you might have spent understanding that system would have been wasted. Finally, most enterprise accounting software vendors don't expect customers to interface directly with their underlying data model. Their approach to support and maintenance may assume you use only published interfaces and features. I would suggest those ought to be the starting point for any data acquisition effort. Good luck with your project!