As for the HDMI to VGA adapter, while I don’t know which direction you intend to connect this, you may not need this. Please keep in mind that the UD-ULTCDL docking station is equipped with a DVI output, which can be adapted to a VGA connection with our included DVI to VGA adapter.
As for the DisplayPort to VGA adapter – this would not be compatible with our dock. These only work from a DisplayPort output to a VGA input, and the UD-ULTCDL dock does not come equipped with any DisplayPort ports.
Lastly, you mention a potential upgrade to 4K monitors. If this is the case, you may want to consider our Plugable UD-ULTC4K docking station, which includes support for up to three 4K monitors. Please see its product page and let me know if you have any additional questions: https://plugable.com/products/ud-ultc4k