Import Data from Sage Line50

This may help

It can be done. How much is actually done depends on the value a business places on having historical data in their new accounting system. How hard it is to do depends on what data is available on the old system and what you actually need to transfer across.

As for general ledger, my understanding is that’s a summary of all transactions. You will need to transfer/enter the data into the appropriate tab/database table in Manager. After which it will be include in the general reports in Manger

The easiest is to only transfer the starting balances from the end of the last financial year. And continue to use the old system for details on the old data. In practice users choose a start date, the real question is how much overlap is used between accounting systems.