You choose a location when you first create the instance. The location can't be changed after the instance is created.
Multi-regional backup locations may be chosen, but only for backup purposes.
The option to
choose your maintenance window is offered: you schedule maintenance at a selected day of the week and time, and the order that your instances are updated.
This discussion group is oriented more towards general opinions, trends, and issues of general nature touching the app engine. For coding and program architecture, as well as re-architecting your solution, you may be better served in dedicated forums such as stackoverflow, where experienced programmers are within reach and ready to help.