Hola,
no harm can be done, the amps rating (3.5A) is the maximum output power, the PSU will serve only as much as is needed by the SEQ V4.
Am using a similar switcher on 5V for the SEQ, too, and it is a good solution. But I have not built the AOUT module yet, this is where the switching might be critical - but you are right, probably there won´t be a problem with such a high switching frequency, and filtering with a few small caps :).
Many greets,
Peter