I suspect it would be cheaper to run a single pump. You could check
the power useage.

We run a single pump and have 3 upflow barrels feeding our two berm
pond sets and two waterfalls. You can easily regulate the flow with a
T and valves between the pump and the veggie filter and falls. Our
pipes are 1 1/2 inch (another time I would go with 2 inch upflow pipes
to reduce the resistance). We have ball valves that we simply adjust
until we have the flow we want. They are set up so that we can run
all of the water anywhere we want (all the pipes are 1 1/2 inch). In
the winter, we run the veggie filter flow by pipe to the base of the
waterfalls. That avoids ice on the falls. In the summer, we have
both berm ponds taking the 45 minute flow rate to grab nutrients and
to do mechanical filtering. The rest of the water is shunted to the
falls or to the bypasses.

If we had one veggie filter and one waterfall, I would split the line
before them and allow for full flow to either. The outflow from the
veggie filter would be easy to run over the falls as well. I would
also set up to be able to bypass the falls if you plan to run the
filter in the winter. Our pump is a pondmaster 2400 gph. It loses
some power by lifiting the water about 4' to the berm and by passing
through a fairly complex pipe and valve system with more 90 degree
turns that it really needs. Still, it holds just fine for our
system. I am set up to be able to put on a second pump (thought I
might need it), but never found it necessary.

A few other thoughts:

1. Have your intake for the pump in the lowest part of your pond.
That way muck settles, fish move it with their tails and it goes up to
your veggie filter. You then have very little cleaning to do in your
pond. Our intake is in a 5 gal bucket with as many 1/2" holes as i
could drill in it. It has mild flow at each hole and nothing too big
for the pump can get into the line.

2. Have your pump outside the pond, Outside is easier to change when
needed. Our first pump was at the bottom of our deep well (old septic
tank) and it meant snorkeling to change it when it gave out after
nearly 14 years. I can do that now, but it will be harder in 14 more
years. Our new pump is immersible and useable outside the pond. I
can change it sitting next to the line. We have a ball valve between
it and the pond to stop the flow if we have to pull it. It has
fittings on either side to allow me to unscrew the fittings and remove
the pump. EASY CHANGE!

3. Have the pump below the water level but above the bottom of the
pond. Below the water level allows the pump to be primed by normal
gravity flow of the water. Being above the bottom means a break will
not drain the pond and strand the fish.

4. Have the pump where its noise will not be a major problem.
Immersed pumps are quiet. Our external installation makes very little
noise and I have baffles to pick up the noise.

Our system is on our webpage (cf Google profile). I don't know if it
is helpful, but it is there. The pics are old, but the plumbing is
still the same.

Enjoy your project!

Jim