Yeah, Paul certainly diverges from the Republican mainstream on a lot of things. He would, however, support a constitutional amendment as the preferred means of prohibiting abortion. Possibly not using prohibitive language in the amendment, but defining "life", which would then cause any state laws that legalize abortion to be challenged on a constitutional basis.

I'm torn on the gay marriage thing. It certainly doesn't seem like a constitutional amendment is the way to go. The problem is that marital status has all sorts of legal and tax ramifications. What you might get is a situation where a state recognizes a marriage, but not the federal govt. (i.e. for the purpose of federal taxes). Or where a state recognizes a marriage, but some private entity (see: employer, or insurance company) does not. Up until now, both groups (federal govt, private entities) basically worked under the premise that "if a state says you're married, then we'll consider you to be married". That may no longer be the case, going forward.