High energy efficiency through transformers
One large transformer is generally more efficient than two small transformers. It's especially true when the transformers get very small, below 10VA.

However, one large transformer plus some long wiring carrying high current at low voltage could easily be less efficient than two small transformers plus some wire carrying high voltage at low current, it depends on the length and size of the wire. The loss in the wire can be reduced asymptotically to zero by using very thick wire, which is generally not done as very thick wire is expensive.

It will be quite easy to calculate the losses from your expected power consumption, distances between modules, wire size you want to afford, and efficiency data on the transformers you intend to use. Set up a spreadsheet so you can re-run the calculation while changing wire sizes, distances, transformer selections, and compute the cost and power losses for each configuration.