Yes that looks okay to me. You delegate all binning to ASTAP. However I assume you get a shorter execution time if the binning is done is Ekos so the file size is smaller from the beginning. So if possible it is faster to bin earlier in Ekos avoiding disk read/write time.
Yes binning is already an option in ekos, which is separate from the downsampling that StellarSolver or ASTAP does. That is certainly still an option for users.
Binning prior to the file exchange with ASTAP will be the fastest solution. Saving and loading a binned image is much faster then with the original size.