There is no benefit to "normal" water to grist ratios of 1.25 - 1.5 qt/lb when it comes to conversion efficiency. Experimental results show that thinner mashes (higher qt/lb) provide better conversion efficiency, at least up to about 2.5 qt/lb (ref:
http://braukaiser.com/wiki/index.php?title=Understanding_Efficiency#Mash_thickness.)
A mash out for BIAB will only provide an efficiency improvement if conversion was incomplete during your mash. This works because you effectively add additional time to your mash, and you also accelerate the conversion rate during the mash out time because of the higher temps (at least until the enzymes are completely denatured.) It would be better to just insure that you mash long enough for complete conversion, and then skip the mash out. You can determine if your conversion is complete by comparing the SG of the wort in the mash to the table found here:
http://braukaiser.com/wiki/index.php?title=Understanding_Efficiency#Measuring_conversion_efficiency.
My advice is to crush fine, use all your water for the initial mash (unless you plan to sparge), and mash long enough to get better than 95% conversion. Keep it simple.
Brew on