It depends on lots of things.
Do you have adults, children, pets that may wander in while you are using your laser? If yes, I would recommend complete enclosure with a shielded viewing window.
If you are going to restrict attendance to yourself only and don’t have windows in your work area, then you can get by with the glasses if you are careful.
No. Not for laser work. If you want to upgrade to the X-controller for spindle work or just want to upgrade for convenience, let your pocket book decide.
I would recommend using my version of grbl 1.0c with spindle and laser support along with PicSender ($25 license) for convenience in switching between laser mode and spindle mode.
You can use grbl 1.1f with PicSender the same way, but I do not recommend 1.1f for laser work.
Think about how you are going to use the laser. Straight engravings work, 2.8 or 3.8 watt, budget decision.
If you are going to do raster image work the 2.8 watt version has a smaller spot size which would give you better images.