That machine looks a bit flimsy at larger sizes.
Given you want to work with full sheets, the machine will need to be a tad over-size. Consider the weight bearing capacity. If you have not used CNC before, when you start, the first realisation things that occur are along the lines of wow!, and why didn't I start using this CNC stuff before? Having said that, do not undersell yourself on what you think you need.
In addition to the machine, you'll need some tooling. Perhaps vacuum holding and dust collection, jigs and various other stuff. Many of these can be made on the machine but they take time and effort so consider this as part of your time/availability budget too. Also, you'll probably be drilling lots of holes? If so you will want full control over spindle speed so a good VFD spindle with the right CNC controls.
Think about expansion and the future use you might be able to get when you get familiar.
Sign making needs some fairly close/consistent tolerances WRT DoC to get good results for engraving/etching, especially if using composite materials.
There are software products out there that address sheet use/production (SheetCam comes to mind but never used it). Other products may be just as useful for your needs, some Opensource and some not. Lots of research for you to do, then perhaps ask more questions.
I'm sure you realise this, but products made from sheet material (flat-pack concept) are sort of like a jigsaw puzzle, so some simple 2.5D software may be adequate.
Have a look at a 2.5D software product called SImplyCam from MR-Soft Nc Software Tools - you can download and have a play with drawing stuff quickly and easily without a license (which is only about $50 anyway), but it would be ideal for the type of work you describe (I have no affiliation other than being a Customer).
Apologies if this raises more questions than answers...
Cheers,
HarryE.
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