i always like doing it all at once, but then i do drive a touch harder than a lot of people, if you get discs go for grooved ones, they do eat the pads a bit faster but the also keep them fresh and de glazed, stock discs and performance pads do work together though. and keeps the cost down for the moment, but if you get new discs later its recommended that you fit new pads again as new discs needed bedded in and new pads have a bedding in layer on them.
Brembo is reputable. Like James, I opted for the total replacement as well. I swapped the rotors for Power Slots and the pads for hawks. I hear that Mintex are nice as well. There are lots of nice options out there for you.
out of the pads and discs on sale in the uk at the moment, i would go for the GTT ones ive driven cars with them fitted, they take a while to bed in but they are very very good, i know its not usual to recommend a competitors item, but as i dont sell brake parts yet, if i were you at this point in time thats what i would go for.
minimum for a decent brake set up and fitting is usually over £400 the AP kit also needs fitted so that will tip that up. i know it seems a lot but ive run my last brake set up for two years and its still going unless your out on track they do last a long time and the cost is worth it in the long run.