....and I'm gonna use existing trees to put it up about 30 feet above
ground, 15 feet above my rooftop on a 5x100 foot suburban lot. Power
lines both in front and back of my house, the ones behind are much
higher voltage, but not real high-tension wires.

All other things being equal, am I better off:

1 - Putting this thing up parallel to, or more perpendicular to, the
powerlines?

2 - Having the coax meet the wire at the base of the tree and
grounding it there, or running the coax up the tree and then depending
on the outer braid on the coax for ground purposes? The coax is
grounded at the first termination point at my MFJ antenna phasing unit
using a short, heavy copper wire to a ground rod.

Thanks,
Bruce