The birthing box looks nice - and feeding her in it now will really help get her used to it. It is SO awesome that you can even pick her up and have her on your lap for a short while - she will likely have fewer problems with you looking in on her during the birth since she accepts this much already - keep up the good work!! Most of the pregnant cats I have known delivered when no one was around, had no problems, and were very attentive mothers. Definitely give the mom-to-be extra food and even switch her to kitten food now - she needs the calories and if she is really that small/young, she needs them even more. A suggestions for the birthing box - go to the thrift store and get some old towels (preferably light in color) and use those with some sheets of newspaper under them - these are much easier to slip out when they become soiled and can be thrown away/composted or washed. I have lots of "critter towels" at my house for just such purposes. I conceptually like the idea of shredded newspaper for the "nest" as it is soft and supportive, but I would be afraid a kitten might get lost in it or tangled or possibly even cut. And make sure you have a litter box in the laundry room if you are going to keep the mama inside towards the end of her pregnancy.
As for shots and neutering/spaying, definitely start calling around to your local vet/humane society/animal rescue group now to see if anyone has low cost options available - and if you want to place the kittens, many groups have waiting lists but are able to provide some other resources (like advertising) while you wait. I fostered a momma kitty with three beautiful day-old babies one year - with the help fo the local humane society, the mom was adopted first (when the kittens were 8 weeks old) and then all three kittens were adopted shortly thereafter. And that shredded paper that you don't use in the birthing box makes a great starter litter for kittens - they tend to play in it but eventually figure out what they should use it for.
She is a gorgeous tortiose shell kitty - good luck to you both!