First time brewing a Porter (BIAB) - Need help!

3.2Ltrs of Strike water & 3.49Litrs of Sparge water appears to be approximately correct for your process. Personally if I were brewing this recipe I might aim for higher volumes closer to 5.4L Strike and 4.4L Sparge, but this is for my own process and boiloff rate. As you can see, the exact volumes depend a lot on your own particular process and the water losses at every step of the way. These losses include: the permanent loss of water that you choose not or cannot squeeze out of the grains (perhaps 0.5L), evaporation rate (process specific as you know), cold break and hop material discarded after the boil (also up to you and how much hop material you have, pellet vs. whole hops, etc.).

All of these variables actually make volume calculations extremely difficult for the small batch brewer. I often brew only 1-2 gallon batches, just like you, and even after dozens of batches, I still struggle to get the volumes figured correctly. It is part of the small batch experience. With bigger batches of 3-5 gallons, I always come much closer on my final intended volume.

Regarding pH and brewing salts like gypsum, CaCl2 and baking soda: in a recipe with a lot of dark malts like this one, you should find you need little if any adjustment at all, or in a few cases you might need just a tiny amount of baking soda, like 1/16 teaspoon. Malt itself contains far more salt in it naturally than any additions that brewers might use, and dark roasted malts and crystal malt will reduce pH to the right place on their own. I would avoid adding gypsum or CaCl2 unless brewing a very light color beer like pilsner or cream ale, as these will reduce pH to the proper level in that case. But any beer with any significant percentage of specialty malts really needs no adjustment in most cases.