Flight benefits are active from day one. Sign up for commuter protection immediately (declare a home airport and if you cant make your flights, you are protected... might only be available after probation though-dont remember).
I stayed in a crash pad for two years and commuted before I moved my family to my station (not SFO). You will have to stay in SFO for one year before you can bid out. You will only be able to get to SEA, IAD, EWR any time soon (maybe DEN). You will be on the worst shifts for a long time, but you can trade shifts without management approval so a lot of guys work 3on/4off or 8on/6off and other crazy stuff (good for commuting).
Its a good career, and there are going to be a ton of guys retiring in the next five years. Once you get a good knowledge base and develop your skills, the hardest part about the job is not getting caught up in the mental bull and politics. Just have a good attitude, work harder than most, and try and be helpful and you will pass probation. Im not topped out, but Ive still made 120-130k/yr every year since we signed our labor contract three years ago (I work a lot of overtime though). I work with guys that are making 180k/yr.
They did just announce a hiring freeze due to coronavirus, but I suspect that will be lifted in a few months. If I were you, I would apply to all the majors & freight and take whatever you can get. Senority is king in this industry, and your date of hire will be more important than your social security number. If your ultimate goal is the majors, get in as soon as you can and figure out the rest later. My two cents & good luck!