Congrats! Sounds like fun.

I had a bad experience with a knife valve a year or so ago and changed
all mine out for ball valves. Basically, I had a line coming from the
bottom drain to my pump and my builder had put knife valves on either
side of the pump. I'd power down, shut the valves, clear the leaf
basket in the pump, reopen and start things up again. Until... a
pebble decided to travel to the pond-side knife valve and lodge right
in the bottom groove of the valve. I couldn't shut the flow off
completely anymore, so I couldn't open the pump basket. I should
mention that this pump is in my basement, in a "wet-ok" area, but not
an area where I could let the pond dump for several minutes while I
tried to clear the stone. And, if things went really wrong and I
couldn't plug the flood, I'd end up with 15,000 gallons of pond water
all around me.

I ended up having to go in the pond (6' down), remove the bottom drain
cover, put a compression plug in the pipe for the drain, drain the
line water by undoing the plumbing after the knife valve (sweating
that the drain plug was tight enough since water flow continued), and
finally reaching in and pulling out the problem pebble which was less
than a 1/4" in diameter. When I put it all back together, I added a
ball valve after the knife valve since there was no easy way to get
the old valve off. I use ball valves all around now even though the
knife valve is still on there. One tiny pebble caused so much grief.

I hope your experience is better than mine in that respect. : )

Dave