I thought I would respond to your request by saying that i would love to help build an arena of sorts, possibly a spleef arena (every good server needs one!). Also, I have a fair amount of understanding of mine-cart systems (however the vanilla sort, not railcraft). Additionally i thought i would answer your questions:
Have you done any SMP server builds before? - Yes, however not as an organised team.
Do you have pictures of your builds? - Not at the moment however, if requested i could get some.
How long have you been playing Minecraft? - A little over a year and half (since the first ne