As someone go let go of a black c63 and his ex wife in one pass, my hats off to you friend. Trust me, it'll get better. (I had to go from that to mini to 135 to m3, but that's my story).
FWIW, I just bought a 16k miled e90, almost all options PLUS about 26k in aftermarket (Dinan everything plus akra evo) parts and that package was a ridiculous $53k with the 26k in parts. (hell, the car included an additional TWO sets of wheels - all OEM).
So what the others have said, 53k is sound - but remember, there are cars like the one I just found out there that will vie for your sale. A more realistic number is going to be closer to the $47k range based on what I've seen (SORRY! don't shoot the messenger!). Go into the dealer/sale subsection, there is a prices paid for used thread. It may help.
In the meantime, don't let lawyers tell you that you need to do full accounting disclosure, fight that as much as possible and TRY to do as much as you can between the two of you. Otherwise, the only ones who win are the lawyers.