Someone else can probably chime in to confirm but I expect that the centre strip of the guitar would be solid. Have a look at my scratch tele thinline build and you will see the inside of my one, I would expect the pitbull kit semi-hollows to have similar chambering.
With regards to the string through holes and whether you should do it yourself, do you have access to a drill press?
Here is some useful links for drilling string through holes.
https://reverb.com/item/1008819-tele...e-luthier-tool
https://www.tdpri.com/threads/drilli...s-help.704327/