The improvements you envision will s@ck less.
Read for a while. The book Koi Kichi of course. Find one and order it. Wade through the Best of Bito here. That's good reading too. Answers will pop into your head.
Depth, volume, circulation, aeration, bottom drains and effective mechanical separation. There are no brand names mentioned in the above list, are there? Nope. They are concepts. More? Stability, resilience, convenience, mineral reserves, protection, nutrition. Blah, blah, blah.
Oh yeh, beauty, serenity, connection. Let's add those.
All of these can apply to a 500 gallon pond, but you will actually need to be more on your toes managing your pond than a guy with 5000 gallons. Good luck in your endeavor.