Starting with tests is usually a better first step. Mostly functional tests are easiest to write. If you can find parts to replace into separate services, tha

Starting with tests is usually a better first step. Mostly functional tests are easiest to write. If you can find parts to replace into separate services, that is best. So you can slowly migrate the system, whilst gaining the benefits quickly for the new code. That way, if the project takes a year, bug fixes can happen in the new code. Also features can be added to the new code. Also, if after a year and the old system is still being used, then valid questions may be asked about what use the new system is. YMWNV