In astronomy, the power of stereo vision is enhanced the
further the detectors are from each other. The NRAO Very
Large Array is a great example.

So, the idea here is to launch 2 space based telescopes
(outside of our atmosphere). One will just orbit the earth,
staying close. The other
will follow Earth's orbit around the
sun, but be 90 degrees out of phase (trailing behind us 3
months).

Then, the 2 telescopes can be instructed to point at the same
region of space to collect data, and be approximately
1x10^10 meters apart. (~100 million miles).

That extremely wide stereo view would give us faster insights
into what's out there, and what's in between us & the targets.

L4 & L5 (2 of the 5 lagrange points), are already in
the same orbit as Earth, just out of phase a few
degrees (not 90 exactly) (in the Earth/Sun simplified
system).

I simplified it as "90 degrees" in the same orbit to
avoid fellow HB readers from looking up Lagrange
points & getting their heads wrapped up in that
math.

You are thinking too small. Put both telescopes on course toward the
Oort Cloud, using solar sails. The niftiest thing about a solar sail is
that if you have one big enough to counteract the gravitational
attraction of the Sun, it will work to do that at ANY distance from the
Sun. (Both light-pressure and gravitational attraction diminish in
accordance with the Inverse Square Law.) A slightly bigger sail will
let you increase your distance from the Sun. So, you can send the
two telescopes on courses that are, say, 175 degrees apart, they
can retract a little bit of sail and hover at any point between launch
and the Oort Cloud, and the Sun basically won't be in the way.

// to avoid fellow HB readers from looking up Lagrange points //

There's your mistake, right there. What about the ones that already
know, and don't need to look it up ?

If you post any idea involving orbital mechanics, then inevitably
someone is going to mention LaGrange. We note that a solar sail has
made its appearance. A diversion mentioning Project Orion, slingshot
orbits, and space elevators will now inevitably occur.