Sway Bar Size & Setting up for Autocross

So I have been thinking of doing autocross next year, mostly just for fun since there are a lot of timed events like that locally but I literally know nothing. So I've got a few questions and could use some advice

So first question:

Whats the stock sizes for 2nd gen sway bars?

I currently have 19mm front and 18 mm back with polyurethane bushings and stock end links

 

Was it an extra option to have the brace running under the back seat of our cars?

I've only seen a few cars with them but I don't know if I should still do strut braces or if that brace would be a good substitute.

 

Just so you know what brace I'm talking about

 

And then any suggestion on tires?

I've got 4th gen 5 spoke 17x7 wheels and was thinking of getting some sticky road tires, maybe Potenza S001 or RE760

 

I won't be doing coilovers since I live in the mountains so ride height is going to stay the same for now

Wow I didn't even know there was a reinforcement bar there! I would still get a rear strut bar, I'm not sure which ones will fit but I would assume they aren't too expensive. that would really help considering you are on stock struts etc. If you did coils you could set the ride height up high and set the preload of the springs as to still stiffen the car up! And I think outbacks came with a rear 18mm and a front 19mm. But normal legacy's like yours came with smaller stock, I believe.

REad up on your AutoX rules...suspension and wheel/tire mods may change your classification...if if matters. Some just do it for fun - not points - so they don't care.