For me the back was quite easy to do, apart from some places.
I had the whole thing done in about 3months or so broken down into 3hr sessions.
I found the parts that are your "love handles" was the most painful aswell as when i had a 3hr session on my butt cheek. I went in with an idea my artist drew up a couple stencils for my koi and then drew the rest straight onto my back with a texter, then he altered a couple things and we went at it.
He was very quick throughout the whole thing, about 1hr to stencil the koi, about 1hr to put everything on my back. around 1.5hours to tattoo the outline.
I then just went back everyweek or so for a 3hr session and it was finished pretty fast.
I don't like seeing unfinished work so i need to go back asap till its done.