I posted before your post came up explaining the custom strat pickguard. You'll be fine. (1 minute late if you look at the time stamp!)Hmmm...second person to give this warning. Maybe I am missing something.
As for the screw size to use, I think you'll be fine with #4's but the mounting hole in the pickguard for neck may be a factor for what fits best.
I have a similar guitar, but with 1 volume, 1 tone. I bought a strat pickguard blank and cut the holes myself.
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