Hi Brando. Welcome to the forum.
Some comments on your post:
An AHI of 12 is in the mild category. You should be able to improve it with a CPAP, but a dental appliance may be another option.
To my knowledge there is no such thing as a non humidified AirSense 10 because the humidifier is built in. You have to pay an optional extra cost to put a cover on the humidifier to use the machine without a water reservoir. That said the heated hose is an option extra. Not essential but it can be a convenience and comfort benefit.
You are correct in that the ResMed Airsense 10 AutoSet is probably the best machine on the market.
I can't help you much with the US DME system as I am Canadian.
The difference between a fixed pressure CPAP and an auto APAP is about 10%. You are correct in that it makes no sense to buy a fixed pressure CPAP. even though you may end up using it in fixed pressure mode, and that is quite possible. The AirSense 10 AutoSet for sure can do auto mode or fixed pressure mode.
Again to my knowledge there is no option to buy the AirSense without a humidifier. The ClimateLine heated hose is a $30-$40 option but the humidifier is not an option. The price for this machine with humidifier is about $800-$900 depending on whether it includes a mask and heated hose.
A prescription is required to buy a new machine in the US, but not a used machine. A prescription is required to buy a complete mask, but not mask parts from which you can make a complete mask. Second Wind sells both used and new machines. Prices seem to be higher in the US than Canada, from my limited look in the US, SecondWind seems to have good prices.
Getting a mask that works is very personal and is influenced by the pressure you need, and other factors such as ability to keep your mouth closed when sleeping, having a beard, etc. What mask are you using now, and what are your concerns?
SleepyHead is software used to monitor you progress. It is well worthwhile to use. Just make sure that you buy a machine that is supported by SleepyHead. The AirSense 10 AutoSet is.
Hope that helps some. If any more questions just ask. I understand when you are new to this, it can be quite intimidating, and the sleep clinics can try and take advantage of you, if you are not informed.
Edit: The comments you make about buying the machine without a humidifier and it being an extra $180 for one sounds like the Respironics DreamStation machine. That is the way it is sold. It is a good machine but IMHO an inferior machine to the ResMed AirSense 10 AutoSet.
Thanks again for the advice here, I've been on the Autoset for 3 weeks or so now. Still fighting through the adaptation phase, but getting better and better. 4-6 hrs of therapy is starting to become more common than 1-2. Unfortunately, I'm starting a trend of using Afrin before bed, otherwise the nasal mask feels suffocating if I'm even the slightest bit stuffed up. I've noticed nights where I've used Afrin, I can put the mask back on if I wake up and it's gone missing, but I seem to always be unable to without. I will say that the nights I get 4+ hours logged, I feel MUCH better than I have for the past year or so.
I'm thinking of trying a full face mask, but I'm a side sleeper, and everything I've read says they are all terrible for that. I'm tempted to spring the $150 to give the Phillips Dreamwear (full face) a shot.
I would try the 3M Nexcare Gentle Paper tape over the mouth. It may help you keep your nose clear. Also, are you using the Auto Ramp, and a start pressure of about 7 cm, with EPR set to 3, and Ramp Only? That can avoid the suffocating feeling.