seat time seat time seat time.
i think the mods you have should be fine for now. i'm really against modding the crap out of your car for the sake of being competitive. that's only going to hide bad habits and in the end you'll still be slower than you could have been if you worked on driver skills first.
but if you must mod the car now, then suspension and tires is the name of the game. it
all depends on how serious and competitive you want to be? national level? local level? the focus can hold it's own locally, nationally, that's another story.
koni yellows and h&r race springs will be perfectly fine for local events. coilovers may be overkill at this point. you will want a rear sway bar for sure. it helps with the wrong wheel drive. i'd say a 23mm rsb paired with an SVT front should be fine for now.
IMO a harness is very important with our cars.. our seats don't hold you in place very well.. SVT seats do help, but i still need a harness with mine. upgrade your brake pads, hawks will give you the bite you need/want. bushings will help.
oh did i mention seat time??
at the end of the day, go out to as many events as you can, let experienced drivers slide your car around and you will see what the limits are. ask questions on what lines they are taking and remember, slow in, fast out!