@andybeerbelly I have only done BIAB since beginning, and though I do NOT consider myself an expert, I've had good/great luck with all of my roughly 200 gallons of beer thus far. Without knowing the amounts of your pale, amber, & crystal malts, we won't be able to give you any range of gravities, but some simple web searches can get you a pretty good idea of your target numbers.
All of this info is for 5 gallon batches:
I typically mash in at 67c (153), which brings my mash temps down to 65c ( 149). I've found I get great "fermentability" out of this temp, and the brewfather app seems to suggest it as well. I've experimented with "mash out" rests, but in my own LIMITED experience, could never tell the difference in the finished product, so my routine now is to finish the mash and crank the heat to max after the hour is complete. I do no sparging or lautering. Those additional steps defeat the purpose for doing BIAB, in my opinion.
I pull my bag of grains (whatever your method is) and sit them in a colander resting over the kettle allowing them to drain as the wort heats. I squeeze the grain like it owes me money to remove as much wort/sugars/etc from the grain and once I feel it's decently drained I sit the bag and colander to the side and continue heating towards boiling.
There are tons of numbers you could be checking here, and once you get your process right, I suspect you will want to - but again, my "sloppy" methods work to produce beer, not great beer, but not terrible beer. Once you figured out this part, then you can begin to delve into the scientific aspects of brewing. I'll probably get flamed for saying this, but it isn't super important to me.
Boil your wort for an hour, adding your hops at desired intervals.
Chill using your copper coil as cool as you can get it. My water gets down to 22c (72), so that's when I transfer it to my fermenting vessel. I pull a sample during the transfer to use for gravity testing (sometimes) or use a refractometer to get your original gravity. Add your yeast, cover your fermenting vessel with an appropriate airtight lid with airlock, and place in a temperature controlled room. My fermenting is all done in kegs under pressure, and that is a different process not applicable to the BIAB method.
If your room temp is right, you should expect fermentation to begin in 12-48 hours using the usual ale yeast. If you have no method of drawing a sample, I fully recommend you wait 2 weeks for fermentation to end if you are bottling your beer.
You mentioned bottled beer was flat and tasteless - did you add sugar to your fermented beer before bottling? Did you use carb pellets? If you simply added your beer to the bottle, there may
possibly be enough active yeast and sugars available to carbonate, but I would imagine it would take months to get to the desired level. Are you letting your bottles condition for a minimum of 2 weeks before chilling and sampling?
I 100% agree that brewing beer has a lot of details that should be addressed, but I also know from experience that someone can make a very decent drinkable beer with minimal effort as long as the basic steps are adhered to. When it comes to bottling, I highly doubt the BIAB method had anything to do with your flat beer.