These are fun ideas. Of course, temporal paradoxes are a red herring I think. If one takes the Everett-Wheeler many worlds interpretation of quantum mechanics seriously, there is no problem. If I go back in time and impregnate my own mother, this happens in an E-W parallel world, causing no paradox with respect to the world wherefrom I originated. The only "rule" I think is that whatever I do travelling back in time along parallel worlds is I musn't increase entropy "back in time" to the extent that the "net increase in entropy" across all worlds is negative. However, since time travel probably is an infrequent occurance, the entropic effect is likely negligible, so, basically there ends up being no way I can harm the laws of physics, etc. thru my time traveling. So in brief, to one and all I say, happy time travelling!! :-)