I can answer some of your questions.
I believe the oil is a special oil. The compressor comes with a bottle of oil that you use to fill the crankcase. How much it costs I can't say as I haven't bought any yet.
The Alpha filter cartridges cost $39.00 from Joe B. I know because I bought 2 of them a couple of weeks ago. The original cartridge that came with the Alpha filter was black plastic so I can't say what was in it without tearing it apart. The ones I recently received are clear and contain both active charcoal and molecular sieve beads. Also visible is a blue strip of humidity paper. I would guess when the paper turns from blue to pink it's time to change the cartridge which is disposable and not meant to be reusable. How long the cartridge will last, I can't say yet.
But before spending $400.00 on the Alpha filter I would suggest you read this thread,
http://www.airgunnation.com/topic/high-side-chinese-filter-dryer-hack/ . For less than $70.00 delivered it is a cheaper and slightly larger alternative to the Joe B Alpha filter. Add a few fittings, a bleed valve, and make a refillable filter cartridge out of 1" clear schedule 40 pvc pipe, and you'll save yourself a bunch of money on both the filter body and filter cartridges. A pressure maintaining valve, like what is included on the Alpha filter, isn't necessary if you're topping off a tank that is already pressurized at 2000+ psi. Now if the tank was empty or near empty a PMV would be useful to get more water out of the compressor air before it gets to the air tank.
Parts? Hopefully Joe B carries parts otherwise you'll be dealing with Chinese manufacturer. And just so you know there is no parts schematic included in very simple manual that comes with the Carette.
When a rebuild might be required? That is a very good question that I don't think anyone can answer right now because as far as I know, no one has enough hours on a Carette to know what might fail. But time should answer this question.