Conditional Autofill, Auto-agregator across multiple tabs?

A small representative sample would be a good idea with a further sheet outlining your "desired" results sheet setup & results based on criteria entered etc...

Formulae / VBA ... conditional work across worksheets in Formulae is invariably "expensive" and cumbersome so I suspect VBA will indeed prove the way to go.

My own advice / instinct would actually to be to think of running VBA that consolidates the town sheets into one central data table with each transaction storing an additional field - town.
From this central table you could then run a standard pivot table which would give you immense reporting flexibility without need for any formulae whatsoever (and ability to "drill down" into the aggregate figures for transactional breakdown etc...)