As you already have a continuous GND plane, and with zone settings that let the GND plane sneak in between the 0.1" header pins there is no need for a any of the via's, nor for the GND plan on your "Front" layer. But it does not hurt your design either.
A very slight improvement may be to use the "Front" layer for a +5V plane, which will form a distributed capacitor with your GND plane. But such thins only become usefull at much higher frequencies (HC TTL is an old an "slow" technology.)
spudboy488 is seeing the square question mark symbols because the project-cache.lib is missing from the zip file. This library contains cached versions of all schematic symbols, and it is an important file you should always put in your backup / archive of a project.
On my system I can see the schematic normally, but that is because I have the same library setup as OP. spudboy488 apparently has another library setup, and when KiCad can not get the schematic symbol from any library it shows the question mark symbols.
This is expected to change in KiCad V6, where copies of the library symbols will be embedded in the schematic file itself in the same way as footprint copies are now saved in the PCB file.