A few years ago, a friend (who became one after buying art from me) and another friend of his commissioned me to do a wedding portrait as a gift for a couple they knew who where getting married. They asked me to do very specific things in the picture. They wanted classical ruins, a red roofed castle, specific clothing and all 5 of the couples cats...oh and a dragon. Well, this was a large canvas (30 x 40 I think) but that was still a lot to cram into one picture and not make it look bad. I also had to work from photos of the people who I had never meet. Photos taken secretly as this was a surprise gift. In the end I think it came out well all things considered and the couple reportedly loved it.
On a side note, when I finished it, the people who commissioned it asked for one change. They thought the woman looked pregnant (not a lot, just a little). So I slimmed her tummy just a small bit and everything was good...but then it turned out, she WAS pregnant! Commissions are hard, some ask for to specific a picture and I can't work well, others give me no guidance, which is also hard to work with.