Gate pull-up/down is done by devices with minimal length and relatively small width, not wider than 1um. To make it stronger and more confident the multiplier of the devices can be increased, but one device should be enough to sink any reference current, if it is not possible to switch that current off.
For current DACs it can help if the size of the switch is matched to the source or to the cascode device, normally small even multiplier is enough, it will have layout benefits. Keep the Vds of the switch device under its saturation voltage in the worst case corner then it will be fine and won't cause headroom issues, and use smallest length. The last is totally related to applied current you have just mentioned, shouldn't be hard to fulfill, and another consideration is that you probably use a digital cell to drive the switch which should be comparable in size with the switch to eliminate big delays. If it isn't, use chain of increaseing buffers,inverters to force drive capability for the switches.