There will be an effect on the
lower frequency antennas by the higher frequency ones and putting up
all the
wire will get you closer on the first try than putting them up one at
time
and tuning them will. ..................................

Myself, I think starting with the low band, and building up, is the
best practical method. You can still do them all at once, but I'd
tune each in the ballpark first, starting low,before I moved to the
next
higher band. Note your later statement...
" The 80m dipole acts just about the same as if it was the only dipole
up
there, but the 40m dipole is strongly affected by the 80m wire."

It's almost always the higher band that will have problems, as this
example shows. It will be very rare for say a 40 to mess up a 80 ant...
But quite common the other way around.. So being thats the case,
I always start low, and work up through the bands...You can always
fine tune after it's all done...I usually do in fact....
Like you say, if the dipoles are at right angles, there is almost no
interaction...In fact, I've had a leg fall down before, and not effect
the match of the other bands. I always spread them apart with the
widest spacing I can...IE: right angles if two bands...
Stacking them like that example on the web page is the worst way
to go about it as far as coupling problems. But....Once you get one
tuned, they will work...I just prefer spread apart...


Also it is not long enough for
the 160m but the idea is to go diagonal and then across at the ends
like a
'Z'. .................................................. ...

That's what I'm using here. I'm on a city lot, so 80m is the largest
dipole I can put up in a straight line. I have a 160m "Z" dipole. It's
a
better compromise compared a loaded dipole to fit 120 ft. I have
the 160, 80 and 40 on one feedline. I have extra insulators to
turn the 160 into 20m if I want....I do that sometimes in the summer...
MK