Research, research, research. Learn all you can. These folks here have some pretty powerful information.
Here are my suggestions:
1. Be your own advocate. Don't take anybody else' word, know what you need and want in a machine. Talk to your doctor, nurses, etc to understand what your machine needs to do for you.
2. There are several masks out there, and the one you need to use is totally up to you. I played around with three different ones before settling on the one I use.
3. Humidifier tanks, hoses, masks, mask gaskets, filters, etc. Amazon is your friend. Use the order confirmation or shipping receipts to bill your insurance.
4. The first month (or three in my case) will be a bit frustrating as you get used to using the hose. Don't get frustrated and stay with it. I was ready to use my machine for a boat anchor after the first two weeks. Sleep lab people told me I would just strap on the mask and dream of unicorns and strawberry fields. Yeah, right. Just stay with it.
5. Direct medical stores are seemingly convenient, but they will own your soul if you aren't careful
Keep the ORIGINAL Rx. Give the DME a copy. That Rx is good forever...at least for a few years.
Reformed CPAP Outlaw