I have been BIAB for some time for similar reasons.
How long is a typical BIAB brew day?
My setup is an large kettle with a spigot, an immersion chiller and a bag that fits well with a drawstring around the top of my pot. I use an electric stovetop and usually get my water up to temp in 15-20mins for mashing, mash for an hour, squeeze out the bag 5 minutes, bring to boil 15-20mins, boil 1 hour, use immersion cooler to cool wort ~15mins, transfer to carboy 5 mins, cleanup 30-45mins. So in total around 4 hours. Doing a normal setup you would have sparging an additional 30-45mins and longer perhaps depending on your setup, mash or alternative approach. So you save maybe an hour.
What (if any) are the major drawbacks to using this method of brewing?
I haven't really found an drawbacks. One possible drawback would be efficiency but I haven't had a problem with that yet and have brewed big beers. I love this approach to brewing.
How large a volume kettle am I look at to brew 5 gallon batches?
I usually don't have much loss because I squeeze as much of the liquid out of the grains in the bag. This means for 5 gallon batches a normal 10 gallon or 8 gallon should do fine and I would suggest starting with 6.5 or 6 gallons of water.
Any tips or tricks to getting the best efficiency out of your BIAB setup?
Firstly, strip often when mashing. I stir vigorously every 15 minutes. This goes against what some people do for mashing because they worry about disturbing the grain bed.
Second, for a while I didn't squeeze out the bag and then tried tried squeezing the liquid out of my bag using my bare hands. Wort is hot in case you don't know and that can be painful. Get some gloves. But also there really didn't seem to be a big difference in the amount of tannins of tannin like quality to the beers where I squeezed out the bag.
Also I tried running 150 degree F water over the grains and it didn't really help much either in terms of efficiency so I don't bother. I have been setting my efficiency at 65% when I plan beers and have been getting something more like 70% efficiency which is quite good.
Are there any changes that need to be made to the recipe in order to make the recipes "work"?
I have been able to use recipes directly the only thing I usually do is lower the efficiency to 65%, but that may not be necessary you might be able to test that out. I don't mind my beers having a little bit more alcohol.
Hope you try it an like it. I know I have been.