Is it possible to get more current from a single output by combining outputs.
For example, I need 450 ma at 5V. Can I somehow combine VR4 and VR1 to get the combined current output?
This generally is not recommended. You can run into stability problems and the outputs are not at exactly the same voltage, it can cause allt he current to be supplied by one output. If you need 400mA at 3.3V, try maybe the HMC976. Its a single output device, programmable output (requires I think external resistor divider), and provides up to 400mA. Is that enough current?