I know ponds generally have a totally different train of thought on filtration... but I run nearly 4000gph on my 200gal fish tank, so 3000gph for your 3000gal pond might be a bit slim.
I'd run some numbers on heating it before even considering fish that need warm water. Dunno what the ambient stays like there, but a pond is large, and open to atmosphere and evaporative cooling, so keeping it warm can suck up a TON of energy. Parents might not be all smiles anymore when they start getting the hydro bill. (I'm assuming you're not paying for the power if it's at your folks' house.)