1. No, this broadcast subscription has nothing to do with season tickets.
2. No, you get to watch any preason game live and have access to all archived preseason games. You also have access to all regular season and postseason games since 2009, IIRC.
3 ST MAX is a DirecTv product that is offered to only some qualified individuals who attend certain universities, apartment dwellings, or otherwise are not able to receive satellite signals. I don't think the NFL sells games a la carte to the general public.
The only reason I even subscribed was to watch all Bills games after the fact. Unless, you live on the East Coast, the odds are you will never watch a Bills game live unless it is the national game of the week or it's on Monday or Thursday night. At least I never have since I live in the Southwest. All these games are commercial free and in HD. Last year, the NFL gave broadcast rights to the XBOX 360 and XBOX One. Hopefully, they'll the PS3 and PS$ soon along with allowing TiVo users the same app.
For me, $70 is a great deal for a year's subscription. I love to watch my Bills several times a week and any other games if I so choose.