Wow man. That is a tough/vague question to answer. I know what you are trying to achieve though. What I have learned from my experience, is that it is a combination of everything. Experience, gear, room, experience, experience, some experience, and also a bit of experience. I am no guru, nor master of anything, but I do notice getting better each time. I used to ask myself "how do I get it to sound like that?". The answer lies in the delicate nuances of a mix, starting from the room that each track is recorded in. Then the actual performance to begin with. Next, correct selection of mic/pre, and the placement of them. Then the whole mixing part that, well, can not really be taught. Only learned by experimentation, trial, and error. Absolutely, there are tips that can give direction, but the skill is an individual one that just comes from practice.
The 'airy' feel comes from working of the tools you have, prior to mastering. I thought for sure there must be a magic plug-in for this when I first started. There are some that attempt to fake this, but in the end, it comes from good tone, performance, and placing the performance in it's ideal place in the mix. Mastering will only expand on what has been given in the mix.
If you are using things like the L2, multiband compressor and 316, be aware that adding those things before getting your mix close prior, will only make it harder to judge where you are at. I will typically mix with a L2, just to have an idea where things are going. But I always check without. Adding an effect to your output bus is only misleading what you are mixing, unless you have a clear idea of where you are going. This cannot be guessed without tons of experience. I know I am still guessing, and I have been at it, off and on for 20 years. And by the way, my personal experience/opinion says stay the hell away from a multiband compressor, unless you are trying to 'fix' something. I have never myself seen the need to do this on a master bus unless I was fixing some other guys crap. If your mix is great to begin with, processing will be at a minimum during mastering.
Post up some examples if you would like others opinions. Maybe there is something we can offer.
Welcome to the forum Dawson!