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Larger aggregate just provides more air pockets in the soil, therefore increasing drainage. The particles will have a harder time clumping together, as they don't allow each other to get close enough to form a seal, or barrier. This allows water to pass through more easily. Typically you would want to add if your soil is holding too much water, or not draining fast enough. Honestly, I prefer perlite, even if some of it gets crushed.

Keep the crushed granite in the pathways and the compost and mineral amendments in the garden soil.
Crushed granite/chat will do nothing to improve the soil.

From my research, it doesn't appear to be any different than that of horticultural grade vermiculite. In fact, I have read sources that stated that gardeners get price gouged, and that it was just the same grade stuff. I would always recommend reading to see what it is the bag before you buy. Otherwise, There doesn't appear to be any reason not to use it.

Sulfur: Plain elemental sulfur (or sulphur) is probably the easiest and most common way to make soil more acidic, since it’s cheap, relatively safe, and can be spread on top of the soil. Since sulfur is pretty slow-acting, you shouldn’t apply more than 2 pounds per 100 square feet at a time.
Read the label of the product you use and apply accordingly. Start with one application (fall is best) and then retest in 3 months.
It can take a year to get soil ph corrected, overdosing can be more harmful than good to take it slow.

If your bin has some anerobic parts, there is a chance the leachate contains phenols or alcohols which are harmful to plants. If it has no smell, you can dilute it and use it on house plants safely most of the time.

I would advise what most composter advise; do not use leachate on edibles.

As long as the manure is thoroughly composted, then it would be safe to add it at about 1 part compost to 2 parts soil. I would also add dolomitic lime to it to stabilize the pH.