Nice one, glad you persisted with your plan to make a CNC machine. Steel is a better option.

You can use all that spare perspex to make:
Dust extractor plate, to attach a vacuum to
Safety screen
Side and end pieces around the cutting area to protect the bearings, drive system etc. from excessive dust
See through lid for your control box
etc.

Your choice of static or moving gantry depends on how much area you have in your workshop for the machine, because the static one will need about twice the area compared to a moving gantry type. Your choice might also depend on what you want to make. For example,
For small (say 400x400mm) very intricate work, a static gantry could be a good choice, because it can be made very stiff.
For larger work, there often isn't space for a static gantry, and the same level of detailed accuracy might not be required. A moving gantry is then often suitable.

If you go for the moving gantry, there is another choice to be made depending upon how wide it is. For wide gantrys, say >500mm, you might want to drive each leg directly rather than a central drive underneath. This is to reduce the risk of racking where the gantry skews to one side under load.

Good luck !