Yes on the resistor, but get the right value. In fact, I recommend you get a 100k and a 10k, so you can experiment. No on the comparator. Look up the comparator by part number, LT319A.Is this the variable resistor you are talking about?
And which of these dual comparators(if any) will work?
You can use any perf board and cut it to size. The exact size depends on the inside of your handle.
Ronv is right, concentrate on the sensor and understand how it works. If you can't get the kind of effect you want from a pressure sensitive resistor, you might need to switch to something like an air pressure sensor sealed inside a slightly flexible handle.
That first item in your voltmeter search is as good as any to start learning. Maybe you can borrow one to start.