I wasn't sure whether or not to post this in the Songs forum, as this is less about the song (which I didn't write) and more about the arrangement.  Anyway, this is my version of a song based around a supplied vocal stem:
https://soundcloud.com/kevs-music/namastessong
[Updated link to new mix 17May2014]
 
My contribution
I take no credit for the song itself, although I did make a few amendments to the existing chord structure. All of the instrumental parts were my creations though and were not in the original version of the song. The orchestral interlude is entirely mine too.
 
Varying tempo
The vocal was apparently not recorded to a click track, but to an acoustic guitar, so consequently the tempo fluctuates considerably. I resisted the temptation to make it constant tempo throughout but compromised and made a few amendments so that it does not vary as wildly. Maybe I should have done a better job though. My driving drum pattern makes some of the residual tempo fluctuations a bit too obvious to the listener.
 
Choice of instruments
It's such a fine vocal performance that I wanted to keep the vocal part prominent and not have it competing too much with the instruments. I found a suitable bass sound, 80s-style synth bass, that keeps away from the vocal frequencies without hiding in the background. But I also wanted to avoid everything becoming too smooth. I avoided the obvious DX electric piano which would have been to cheesy an opted for a clunky Wurly instead. The contrasting textures seem to work ok.
 
Arrangement
I stuck with the original vocal stem, but inserted an instrumental section after the second chorus. For contrast between different sections, I used a choir pad on each chorus, a hammond organ (NI B4II) on the first half of each verse and nothing for the second half of the verse. Paradoxically, the "nothing" (i.e. nothing accompanying the vocals other than drums, bass and e-piano) seems to have the most impact. The choir pad ducks the vocals (I think I used Sonitus Gate for that but I can't recall). The third chorus has lots of bits of percussion, noises and hits. The fourth chorus has sequenced synths.
 
Orchestra
The melody for the orchestral interlude suggested itself after listening to the song a thousand times and it was in my head everywhere I went. I also wrote a similar introduction leading up to the first verse but didn't use it in the end.  I used 10 instances of Miroslav Philharmonik altogether.
 
Comments welcome, especially negative ones.

I'm not a big fan of her abilities, I think you did a decent job with the mix. She's a little too wet in the mix (IMO) I would have made the orchestra a little wetter in places :-) It's the wetness that binds us? And divides us...

The Band19
...She's a little too wet in the mix (IMO) I would have made the orchestra a little wetter in places...

I think agree, certainly about the orchestra anyway.  I'll go back and try again. 
 

Kind of a Sade sounding vocalist and groove to this.  It's pleasant enough, I like it.  When the horns first come in they are hotter than the previous music, those strings at 2:54 are real hot and the strings don't seem to have any reverb.  Yeah, the string and horn sections just don't match the vocal sections.  But, I think you can deal with that fairly easily.
 
I hope you'll make some adjustments to the mix and repost.
 
 

Thanks for the pointers. I'm working on it right now.
 

I agree with what has been stated above. I think the reverb on the vocal is not so much about how much you have on it but how long it is ,if you shorten it where it doesn't tail out so long I think it might fix that. Also ,agree that some of the instrumentation sounds a little dry, particularly the piano. Also, agree that the horns are a little hot when they come in. Good job on the arrangement, it is not easy to match tempo and  make things fit well, but you accomplished that..

The wet vocal originally belonged to another project and to an earlier, more acoustic, version of the song. Altering it would be feasible, except that a pad that I have used in the choruses has been set up to "duck" the vocal, so I would need to re-do the pad too. I can't remember exactly what I did or how I did it, as it was 4 years ago. Maybe I'll leave the vocal as it is for now and focus on the other issues.

I'm digging the organ? And the song overall.

The Band19
I'm digging the organ?...

I used 2 instances of NI B4II with almost the same settings and mostly playing in unison but with the rotators out of sync with each other.

Man that's the same friggen trick I use! No wonder I liked it! 
 
And I sweep pan them a bit also slightly out of phase. And I like to actually use two different presets, one is soul explosion, and the other is more percussive, and I also automate the volume on both one up a bit, the other down a bit, and then vice versa, in time with the music. It's a lot going on with just the organ? But it makes it sound fat...