Unless you are going to an SPL competition, the Type R's will do just fine with 500wrms. You will get told they *need* more by people who compete, but they really don't unless you are trying to get them to their FULL potential. With 500 watts apiece, 4 Type R 12's would be stupid loud.
If you go with 4 type r's your gunna need more power... Id reccomend running 2000 watts to one l7 then use the other for when it blows... muahahaha... seriosly though, if youd put more power into the 4 type r's the SQ would be much better.