I think it's much the same, except that an opposition can give more of a see-saw or vacillating effect. In a romantic relationship where the couple identify with Venus, Pluto may be experiences as a person or events external to the relationship who seek to undermine and terminate it. Otherwise Venus-Pluto can get obsessive.
There are cookbooks out there on planets in synastry. You might try Steven and Jodie Forrest's two volume Skymates. It's kind of a lot to go through all of these aspects. Jupiter is generally the "feel good" planet, but in a stressful relationship with Pluto, I think that it, too, could get caught up in a power dynamic. Venus-Neptune can lead to a beautiful fantasy world, but it is not the planet of grounded reality.
In terms of how I'd look at the aspects you mention, I'd ignore Uranus conjunct Pluto and Neptune sextile Pluto, which are generational. Then generally trines and sextiles are favourable, and oppositions are stressful.
A composite sun indicates the heart or identity of the relationship. So Venus conjunct sun is a good indicator of love and affection. Mercury conjunct sun is good for communication, and so on. The ascendant in a composite says something about how a couple appear to other people.
Venus-Pluto can get pretty obsessive. A lot depends upon the maturity of the people involved, however, in terms of where they take this. Negatively it can lead to scenarios where the two have a "dominate or be dominated" feeling about the relationship.