I think that's a fair price for the 4yr service. As of a few years ago they became all-inclusive so the brake fluid change is part and parcel of that price. I don't think you'll get £150 knocked off if you say you don't want it doing, so I'd just get the OPC to do it all.
As for the brakes, they can advise all they like but if they're only worn and not worn out then you're fine to refuse the work. As you say, an Indy can probably fit genuine parts for a cheaper price than the OPC can as the labour will be less. However, it might be worth getting a quote as if the difference might not be that great - some Indy prices have crept up of late!
As for the brakes, they can advise all they like but if they're only worn and not worn out then you're fine to refuse the work. As you say, an Indy can probably fit genuine parts for a cheaper price than the OPC can as the labour will be less. However, it might be worth getting a quote as if the difference might not be that great - some Indy prices have crept up of late!