I think that you need to go through an intermediary step of AEM 6.5. That's because with AEM 6.4 some paths in the repository changed (for example /etc/tags moved to /content/cq:tags and some more things), which the migration tools to AEM CS don't handle.
For that reason I would recommend to go through AEM 6.5 before:
- The changes you need to do (both content- and code-wise) for AEM 6.5 are required for AEM CS anway, you don't waste effort when you migrate to AEM 6.5 first.
- It allows you to split the amount of changes in 2 steps (AEM 6.2 -> AEM 6.5 and AEM 6.5 -> AEM CS); and that allows you to validate your first bunch of changes on AEM 6.5 (on-prem) and gain some confidence in it, before you then migrate to AEM CS.