Since Docker’s overhead is generally negligibly small, you can easily orient yourself on the resources you have previously required.
However, it is advisable to choose a slightly larger Quantum Cluster so that you can also benefit from the flexibility that Docker offers — staging environments etc. are often easy to set up — if the resources are sufficient.
Planetary Quantum Clusters (no matter what size) have no artificial limitations except for the booked CPU/RAM/HDD resources.