What is the optimal solution for converting a database schema?
There comes a point when a step-by-step clean-up becomes more work than a clean slate and migrate approach. System availability and time to migrate may factor in to the decision when dealing with larger volumes but at this size, not an issue.

Key factors for me here are:


Renaming foreign key constraints to fit a new application framework.
Refactoring a significant proportion of existing tables.
Low volume of data.


In this situation I'd be very tempted to design a new schema that fits the model you now require and create the necessary scripts to migrate data across (your option 4).