The std 941 pump is fine up to around 400bhp all day long, the group a 044 pump doesn't actually flow that much more in terms of l/min but does have a much higher lockout rating.
Have you rewired the fuel pump circuit, if not it needs doing now, why £1K for stage 3 ?
You can get a good ecu with complete mapping on three maps for around that, that also does the usual over hyped coil pack and closed loop, personally wouldn't waste my money with the std ecu and being bound to using only official add ons, which are imo a piss take price wise.
At stage 3 you don't need coil pack, a decent coil will do the job fine, closed loop isn't needed IF mapped correctly.
tabetha