It's quite easily to map the accounts once you have the main categories mapped (I use the french naming so my german translation may be wrong):

- Aktiven <-> Assets - Passiven <-> Liabilities - Betrieblicher Ertrag <-> Income - Betrieblicher Aufwand <-> Expenses

I'm not sure I understand what you ask about rollup, but so far I haven't found a case I couldn't fit within Ledger. For VAT, I have a flat VAT rate that only applies to my turnover so it was simple to automate (reduce turnover by x% and put that amount into Owed VAT).