Hey Earle, it is a steep learning curve eh?
Don't stress too much, the beer at the end will be good, even if a touch under strength.
Our set-ups are different. I use a three ring LPG burner under a 50 litre keg with the top cut out, and a camping foam mattress for insulation during the mash. Your set-up sounds ideal, and your method sounds the same as mine up to mash-in. I don't have a grain mill, and buy all my grain pre-milled. If you tell the retailer you are doing a BIAB, they will often double-mill it, but I have had fine and coarse crushes, and found it not to make too much difference. I have a fine-weave bag, so I find the coarser crush drains a bit more readily. They have never charged me a fee for milling.
I generally heat the water to the temp I want to mash in at, then as I turn the flame off, the water will generally rise a degree or two (absorbing more heat out of the heavy stainless keggle), which will then drop back to the desired mark as I add the bag and then the grain. I agitate the mash every 15 or 20 minutes. I usually do a 90 min mash, during which time I lose a couple of degrees on a mild day, and up to five on a cold day. As most of the saccharification occurs in the first few minutes of the mash, I don't tend to worry about it too much, although I have a false bottom in, and have turned on the flame once or twice in seven brews to date.
Your volumes might take a while to hone. Once you have done a few brews you will know how much to allow for loss to absorption, boil-off and trub. I use a calculator from the BIABrewer forum site which suggests what the volumes should be, but I have had to alter my rates of evaporation loss because I tend to have a gentle boil and lose less than others. I can email you the calculator spreadsheet if you like. Samples are taken to check SG pre and post boil, but I usually let them cool rather than correcting for temp.
I had some difficulty raising the bag on my first BIAB, with a slow-drain, heavy bag, gloves too thin to squeeze the hot bag with, and a bag of grain that was bigger than the opening I had to pull it thru. So now I use a ratchet tie down strap hooked from the shed roof, and I can bring it up by degrees as I squeeze it out (with thicker rubber gloves
). I will get a bag with a coarser weave next time. As I start to pull the bag, the flame goes on, so it is technically not a mash-out, but the temp comes up a bit. Once the bag is out, I heat flat out until I have a big rolling boil, then kill the second ring, and maintain a slow boil. I have read that a slower boil doesn't cook off all the hop character from the bittering addition, and may result in better hop flavours, but my primary reason for having a slower boil is that I don't have to heat so much water in the first place.
If you like, check out the BIABrewer forum. The guys on there are passionate about their BIAB.
http://www.biabrewer.info/