This is a monumental challenge. The major focus for me is to prevent further blight, as this destroys the value of all the surrounding properties. This is a process that the numbers, the amount of red tape involved in dealing with the county, and time all have to be addressed first.
These are the stages
1. Acquistion,
2. Demolition,
3. Reconstruction,
4. Disposition.
We must account for all costs associated with buying this distressed property. The numbers have to work.
Any squatters must abandon the property peacefully. Police involvement is not usually an option and requires dealing with the people issue through seeking help from non profits to provide alternatives for the people dealing with the addiction. Eliminate the property at its core, demolish it to the raw land to allow a pathway to rebuilding.
With addiction, removing the people is primary. Bringing the property back to the studs will help, but you still have associated costs and permits. Land is simpler to control while we worked all the details out.
I hope this helps.