Yeah I don't think the RCAs will be needed. The only thing I am not 100% on is the subs, but I don't think the 460 included subwoofers? Don't hold me to it though.
As for blasting the the volume, if you still have OEM speakers then I will definitely say go ahead and get new speakers. The chances of the OEM speakers clipping and blowing have increased like 50 fold (not an actual statistic). The new HU won't be so much the problem, as it is contributing to the problem.