Getting the right exposure for action photography

I've been photographing martial arts for a few months now (nothing serious, just to help promote my school), and I'm fairly new to dSLRs, so I know I have a lot to learn.  Today I was given the opportunity to photograph a day-long tournament.  I experimented here and there, and while I liked some of the shots I took, I was frustrated.

One place online had recommended to shoot at least at 1/320 of a second to freeze the photo with *just* enough movement. Well, I used my 50mm 1.8, and getting 1/320 indoors pretty much required me to be wide open (which I don't mind, because I like to shoot shallow), and I was already at 1600 ISO.

Other places mention shooting using spot metering, which I understand because using matrix metering was kinda throwing off the exposure due to the audience and referee wearing darker colors.  Spot metering doesn't work in Manual mode, so I have to shoot AP for spot metering.  However, using spot metering in AP then doesn't guarantee that 1/320 of a second, and if I shoot in Shutter priority, I'm not guaranteed the shallow DOF.  Also, if shooting sports is best done with spot metering, how can you make sure you're metering the right places when everything is moving so quickly?  And how does one maintain focus with all the movement?  I'm trying to use back button focusing but some of my shots still appear a little out of focus.

Am I overthinking things?  There's just so much to take into consideration and doing all of that while keeping track of the action, anticipating what's going to happen when and where etc. is driving me up the wall.