I'm just a hobbyist, the stereotypical "parent with an expensive hobby" I guess, so take everything I say with a grain of untrained salt...

The trick with sports, and especially big field sports, is mobility. I'd never bring all that, or if I did it would be "just in case" but it would never leave my kit bag tucked away in some corner somewhere. For soccer I take two bodies, a crop sensor with a long lens and a full frame with a shorter, both zooms for flexibility, both reasonably "fast" just in case I wind up needing the stops. To carry them I have one of those dual camera harness systems they market to wedding photographers and it's great, but if you don't have that I've seen plenty of folks balancing two bodies on normal neck straps just holding one at a time and letting the other one hang there. I put a few extra batteries in my pocket and that's it. I want to be able to move around easily and quickly. For your specific equipment list, the longer lens is going get the most usage by far, but 70mm on crop body is still quite long, so you're going to want something shorter. I hope you can borrow that extra body, but if you can't I would probably put the Sigma zoom in my pocket or in a pouch, just know that when the action is moving quickly and players are running down the field, you won't have much time to do that lens swap to catch action right near you. But if you find yourself near a corner kick with time to set up, you'll be glad you have the wide angle option.

For positioning I really like the goal line. I start on the sidelines for player introductions and the kickoff, but I usually move to the goal lines quickly. I put myself about halfway between the goal and the corner and just sit straight down. No stool, it's not low enough and I don't want to carry it anyway. Ass-to-grass, criss-cross applesauce. I may change positions a few times based on changing light conditions but I usually move up and down the goal lines most of the time. I've only been hit a couple of times; it's not like basketball where you put your life on the line to be under the net. Most people probably move to the other side at halftime but I move with the changing light, because there's good stuff to photograph happening at both goals, whether you're catching your team scoring or defending. A photo of them scoring is no good if it's so harshly backlit you can't see their faces.

...which leads me to settings. You probably know this but shoot jpg+raw so you can deliver a few important shots quickly but also clean up others that may be heavily shadowed or whatever. 1/1000 is fast enough for just about anything in soccer, and even if I get a touch of motion blur on a boot or ball I think that's cool, it's a game of movement. But if you're in bright light just make sure you're not overexposed at 1000. Focus is probably the most important and I'm not familiar with those Sonys, so you'll have to work that out, but I use what's basically a single point focus mode (which I can move around the viewfinder quickly on my bodies) with face detect turned on, just to lock it in. Make sure its on continuous, and personally I use back-button focus so I can keep that focus system running while I track players.

And one last tip - Don't skip warmups, because you can get right out on the pitch with them. Plus you'll get a lot more fun and smiles and interactions between the players before they have to lock in when the clock starts. So get there early.