RE: Transferring assets to new books in Fixed Assets
This one can be a bit complex :)
For switching which book will update GL you can change the corporate book in the FA company setup window (Tools>Setup>Fixed Assets>Company).
For creating the import file, this really depends on how they want it handled. Do they want the new asset\book records to have the same remaining life as the current assets? Do they want the cost basis to match the remaining net book values? Do they want new assets entirely to replace the old ones? Etc. Depending on what exactly they want to see will determine how the data needs to be prepared for import.
Regardless, you can likely get a lot of what you will need in SQL from the FA00200 (asset\book) and the FA00100 (asset general, link the tables on assetindex) or from the asset book smartlist. Once the data is processed you can then use IM (with the FA eConnect adapters) EConnect itself, or the FA import\export tool to bring in the new asset book records (or new assets entirely)