Help me plan my first all-grain (BIAB) brew!

I wanted to brew one more time before the weather (and my basement) warmed up, so I was thinking of doing a half-batch of the Stone Ruination clone recipe that was published in Brew Your Own a few years back. Then, for a little extra fun, I thought it might be a good time to try BIAB, since the extract version of the recipe calls for 45 minutes of grain steeping anyway. I wanted to run my plans by everyone here to see if I'm missing anything important before I start. Here's the recipe for a half-batch (2.5G, presumably at the end of the boil):

7 lbs 1 oz of 2-row
7 oz Briess crystal malt (15L)
18 AAU Magnum (about 1.125 oz) @ 90
8 AAU Centennial (about 0.75 oz) @15
1 oz Centennial whole hops (dry hop)
WLP002 English Ale yeast
1/2 tsp Irish moss for clarity @ 15

Mash at 149 for 60 minutes
90 minute boil
Ferment at 68 F
They don't say how long for fermentation or dry-hopping, but I was going to do ~2 weeks and ~7 days

So here's where I have to start planning.

MASHING: I used a BIAB calculator and wound up with 4.45 gallons of water at 155F before adding the grain, which will leave me with about 4.15 gallons pre-boil and 2.5 gallons at the end of the boil. I was going to mash for 90 minutes, since I've heard that gets you better efficiency for BIAB.

WATER: From some links I have read (thanks, @ac24!), I can get a decent water profile for an IPA starting with RO water and adding 1 tsp of gypsum and 1 tsp of calcium chloride per 5G. I also need to replace 2% of my grain bill with acidulated malt, which in my case would be 2.4 oz. I was going to buy a lb of the stuff and then attempt to crush it with a rolling pin or mill it in a food processor (the rest of my grains will be crushed at the store using proper methods).

INGREDIENTS: Since I need 1.125 oz of Magnum but don't want to waste most of an ounce, I though I would make up the missing AAU with the leftover quarter ounce of Centennial, which should be just about right. As for the crystal malt, the store that I'm buying only offers what they call "Caramel Malt (Crystal) - 20L". Will that be OK? And for the yeast, well, I'm really kicking myself for not harvesting any from the ESB that I kegged last week - didn't think I'd be using that strain again any time soon, let alone in a higher-gravity beer. Oh well, live and learn.

So I'll be mashing for 90 minutes at 149F, boiling for another 90 minutes, then chilling down to about 65F before pitching. For practical purposes, I'll probably transfer the wort from my 10G kettle to my 5G kettle after 60 minutes of boiling, since this makes chilling much easier for me and it'll be easier to keep an eye on my boil-off in the smaller kettle. I'll let it ferment in my basement, which is currently at 62-63F ambient - not ideal, but my fermentation chamber is serving double duty as a kegerator right now. Toss the dry hops in the bucket after 2 weeks or so (assuming the gravity is where it needs to be) and then bottle a week later. I'm excited to try all-grain, let me know if you think I'm forgetting anything important.

 

I estimated 1.1 gallons/h, and used the calculator at http://biabcalculator.com/ to get my water amounts. I'm not 100% certain what my boil-off rate will be, but I think this is fairly close, and I can top it off with some extra water if it looks like I'll be short near the end of the boil.

 

When you say "halve your water additions", does 1 tsp of each strike you as too much? The info that I had was per 5G of water, and since I'll be using nearly 5G in total, I was going to go with that. Are you supposed to count the water that boils off or that is lost to grain absorption? I would think not for the former, but maybe for the latter, but what do I know?

As for my boil-off rate, yes, I'm estimating that from my previous extract brews. I don't expect it to change, but I'm also not 100% sure what the rate actually is for my setup.