Are the fiesta st150 and focus st170 rear brake calipers the same??
I’m about to fit the discs, calipers carriers and dust shield off an st170
Not stripped mine off yet but the calipers and pads look the same
Also anyone know if just updating the rear brakes and not the front will upset the brake balance???

I don't know but unless you are running big power beyond 200bhp I doubt you will need an upgrade (unless doing track time), the standard set up is very good, best thing I did was upgraded to braided lines made a noticeable difference to pedal feel.

Got it up to 230hp do brakes do need a bit of help
and will upgrade the brake hoses at the same time
Not sure what to do with the front,
Any ideas?

there are some big brake upgrade kits about, would be everything changed though calipers as well and then you might get offset issues with your wheels catching the caliper so good research needed.

230 there would be no reason to do a full upgrade on the rear, better pads and brake lines would do the same job

Yes, front and rear has same calipers as the Focus, it's the carriers and discs that are different.

Generally you want the more powerful on the front so it could throw the balance off.

Remember, bigger discs increases the unsprung weight, particularly the front 300mm discs on mine are pretty heavy. As above, better pads would be a good way to go but its your call.

4 pot front calipers would be a good improvement but more cost and work involved