You can 100% use xr5 focus downpipe. They sell them as a 2 piece downpipe + cat pipe. You need both from same brand and it will bolt up to stock exhaust.
Don't need a tune for downpipe, just need to space rear 02 sensor.
I've modified full miltek xr5 exhausts to fit c30's but there's a bit of mucking around.
Downpipe+intercooler are best bang for your buck mods.
cat back + intake + dual port make it sound nice