Yes to both, although uninstalling P5 after having installed P7 may cause Windows to lose the file associations for poser files.

I did that, and had to run the installer for P7 again because none of my pz3s were connected to Poser anymore and I couldn't get Windows to accept it as a program to open the files.

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If you're joking that's just cruel, but if you're being sarcastic, that's even worse.