One advantage of f-spaced is that they also have short legs. Some regular spaced humbuckers have long legs that fit in a Les Paul but are too tall for a strat cavity. Since you are building yourself, this shouldn't make much difference.
The JB with a 250K pot (like what is already in your strat) will work great. Seymour developed it for Jeff Beck to use in this exact application. It is hot, but that does not mean it is a "metal" pick up. It is very versatile and can fit in with most genres of music. In a band, it will help...
That is just how that pedal is designed. I had the big version and it did the same thing. With a few exceptions, silicon fuzz pedals are not known for cleaning up when rolling the volume down. However, the Fuzz knob on that pedal was useful.
Most of your wanted characteristics describe a Germanium Fuzz.
If the Sunface is too expensive, try the Fulltone '69 as suggested or a MJM London Fuzz.
Solid Gold FX Rosie is my favorite for a semi-affordable tone bender(about $120 used). I sold the EQD Tone Reaper after I got it. It is more of a singing fuzz than a splatty fuzz if that makes sense.
Ironically, that is the "problem" with poly. Some want their guitar to "age" to look like the relics coming out of the custom shop or that picture of their favorite guitarist with his #1. It just can't happen with poly because it does its job too well.
Guitarists are such a weird group. Can...
• Would I get the same positive results if I just switched from 10s to 9s but kept it in standard pitch? NO. The main positive result from tuning down a half step is that your singer can sing a half step lower. Changing to 9s does nothing for this. Bends on 9s are easier, but I find them to feel...
Wow. I can't believe I am the first to call this out as an April Fool's joke!
If I am wrong, I don't mean to be insulting but mid-scooped is rather self-explanatory. If I am correct, well played and Happy April 1st!