1) OK so far, but it's not necessary to make only a gallon at a time. I have a small utility tub that holds about 2.5 gallons, so I usually fill that level with each of the 3 ingredients & dump it into a mason's tub used for mixing mortar where I dampen it and mix with gypsum & anything else I might be incorporating

2) The gypsum (CaSO4) gets incorporated into the soil when you make it, but the Epsom salts (MgSO4) gets mixed into your fertilizer solution each time you fertilize. Use 1/4 tsp MgSO4 per gallon of solution if you're fertilizing at a reduced strength and at 1/2 tsp per gallon if you fertilize at full recommended strength.

3) Yes, mix while damp, but no need to allow the gritty mix with gypsum rest. Gypsum is much more soluble than dolomitic lime, so there is no appreciable reactive phase to take into consideration.

For most plants, you should use gypsum instead of lime in the gritty mix, but you can use lime for figs if you prefer. The larger pellets of lime and gypsum is the same product you are using, except that it's combined with a binder and 'prilled' so it's easier to broadcast (spread). The prills simply break up when they get wet. Also, you'll be using such a small amount of gypsum that it would be insignificant as far as any deleterious affect on soil structure.

Without some established controls, it's not possible to establish a comparison between a peat/compost/coir-based soil and something like the gritty mix. That isn't to say that there can't be a very significant difference, only that hard numbers are difficult to establish because of the number of variables. Your watering habits and any steps you might take to help mitigate the effects of accumulating salt levels play a major part in how clear the delineation is, but the very large number of GWers using soils like the 5:1:1 or gritty mix and happily sharing their results should be enough to confirm that for most growers the difference could be considered striking.

It's also difficult to separate the effects of compaction and PWTs because they are linearly related. Try to remember that media compaction and the accompanying lack of aeration produce stresses on the plant. Even if nutritional availability is significantly more reliable from ionic sources, supplying nutrients in that form won't noticeably relieve or negate the stress arising from other negative cultural conditions.

Al