Huw

Well with regard to your drivetrian set up i think the bird comes with spider cranks as stock however as i see it there are 3 types of set up you can have depending on where you want to run your freewheel (provided it is external to the hub) 1. spider with arms at the fron freewheel at the back 2. fixed sprocket at the front freewheel at the back 3. freewheel at the front fixed sprocket at the back Most low end bikes run setup 1 and higher models set up 3. I recently went from 1 to 3. However if you wanted to change from 2-3 or visa versa it would not be a problem as both of freewheel and sprockets screw on. As you are buying cranks you now have a choice of what to run weather you get spider cranks or threaded. (Also sounds like you have a square tapered bb so make sure you get the right ones.)I recommend 3 as it has weight saving and positioning advantages in terms of chain and freewheel and allows better clearance for a bash plate, although I do not yet speak from experience of this setup, just what i've read. My comment about base width, is when I stripped the hub the sprocket is obviously attached to a round collar which is threaded to screw on, therefore the wider the base the more threads in contact and the lower the force per thread making it less likely to strip To start out buy maxis creepy crawler tyres from chian reaction cycles, I found them the chapest and there pretty good especially at the price. Hope this helps

Depends if your looking for used or new stuff? If your looking for new then tartybikes are the best place to start they have pretty much everything, however second hand try pinkbike and ebay (alright for new stuff too). On a side note i started running front freewheel the other day and I found second hand cranks are very hard to find if thats what your lookin for, and i assume u want a screw on sprocket? Make sure it has a wide base or you will do as i did and strip your threads on your cranks or hub in a matter of minutes hope this helps