I would get the Central Line from the DLR at Bank rather than walk. It's a bit of a hike between the platforms, but then it also is to just get from the DLR out to the surface (especially at the moment when the escalators are being replaced), and then to know which way to walk.

In case you aren't aware the area round the Andaz (the old Great Eastern Hotel in Liverpool Street) will be pretty deserted over the Easter weekend, apart from the Sunday morning when Petticoat Lane market is open. It's completely safe, just that almost nothing is open and everything is a tube ride away. It's part of the reason why the good old Great Eastern (a favourite of John Betjeman) just faded away. Business nights only is not enough at Central London costs.

If you are flying to London City on March 21, Easter Friday, the airport is under curfew not allowed to open until 9am on public holidays to protect the lie-in of the nearby residents (which includes me). Several of the morning flights are cancelled as its a holiday but a number of others all reschedule for a 9am arrival so it is usually a bit of a rush as they all come in together.