i agree with DVDrip... default on the Atomik transaction, pay the relisting fee... the $100 they charge you, is marginal compared to what you will probably need to spend getting the bike up to snuff.
One thing people havent mentioned in regards to buying a PitPro, and then paying exorbitant costs for spares, is that pitbikes (the ones worth mentioning anyway) are of two types... KLX type, which is a copy of sorts of a Kawasaki KLX 110, or the CRF type, which is a copy of sorts of the HONDA CRF 50. When you figure out what sort you have, pretty much all parts are interchangeable between brands, and it's only quality and price that differ... IE: If you bought a pitpro, that was of CRF type, you could purchase your parts from China for a minor fraction of the cost of sourcing the parts in Australia. Despite the fact they came from different store/dealer/ shonky salesman etc, they would be interchangeable to a point... so if you bought a pitpro, found their parts prices a bit much to swallow, you could buy the identical part from DHZ, and it would fit onto your bike...
DHZ are rapidly gaining a reputation of being one of THE BEST stores to deal with, and rightly so....
Given you have never ridden before and are only new to bikes, let alone pit bikes, i'd go with a 125Pro from DHZ.... yes, they're little bikes, but they are twitchy, and even the 140's can bite the novice rider... a 125 would be ample motor to allow you to have fun, learn the basics etc without being too difficult to ride, and still allows plenty of scope for modification at a later date...
Follow this link for a looksee...
NEW 2009 DHZ DPRO125 LIFAN BIG BORE RACING THUMPSTAR - eBay Other Trail Bikes, Trail Bikes, Motorcycles, Cars, Bikes, Boats. (end time 03-Sep-09 08:28:56 AEST)
as for what to do to your bike when you first get it, there are a couple of threads written specifically for the new rider in regards to initial set-up, and performance modifications for non-mechanically minded persons... all the answers you need will be in those two threads.
http://www.miniriders.com.au/bike-setup/24009-performance-upgrades-guidelines-stage-i-iii.html
http://www.miniriders.com.au/bike-setup/24239-achtung-noobs-your-new-pitbike-you-set-up-tips.html
http://www.miniriders.com.au/bike-setup/18939-new-bike-wat-check-before-riding.html
Good luck mate, and welcome to Miniriders!!!!!