Those "outdrive savers" will work, but you'll spend WAY more money than you have to buy buying those. You can go to your local home improvement stores and go to the plumbing section. What you want to pick up are some 5/16 compression sleeves. Not all Lowes or Home Depots have that size (it's pretty small), but I'm pretty sure all ACE Hardware stores carry them. You might spend $1 or so on them.
If you're looking to upgrade from the start, pick up some CVD's. They will get rid of the dogbones and you won't have to worry about them flying out. The axles will be much stronger and won't break as easily also.
If you're going offroad in the dirt a lot, pick up some scrap lexan sheets so you can make dirt sheilds for your chassis. The 18T is very open to dirt and pebbles being thrown in the spur gear. You won't get far before you're replacing spurs.
Your gearing will depend on the track you race on.