Welcome to TFK!
If/when you have nitrates around 5ppm or so, I call it a win. You might find value in gravel siphoning unplanted areas. Also, pea gravel seems a bit coarse to me (allowing uneaten food and waste to drop below and decay) and perhaps a finer substrate on the surface would be better.
Also with respect to nitrogenous waste, the food quality makes a big difference (you already have this somewhat covered). Some fish foods use lower quality fish meal in their 'recipes' requiring copious amounts of starch (wheat, oat, soy, rice flours) binders and to increase crude proteins. But much of this just passes through the fish. I discovered when I switched to Omega One and Ed's Almost Natural (both use fresh, whole fish) that my fish suddenly produced less waste ... believe it or not
And...it goes without mentioning to ensure your not over feeding.
Now I don't really buy into the (video) need
for a sump/refugium as I'm seeing success with a simpler bio-filter...
I have two Aquaclear 70 HOB filters on my 60g. The first is a dedicated bio-filter. It uses an AC20 impeller for reduced flow. It has a thin, coarse pad and is filled to the rim with a packed mixture of Seachem Matrix and De*Nitrate bio-media. I rarely touch this filter to ensure the stability of the media/colony. The other filter is strictly mechanical with a sponge and tightly packed polyester fiber. I clean this filter often. I've also been using Seachem Purigen, a synthetic scaveger resin that adsorbs dissolved organic compounds and is regenerated with a 50/50 mix of chlorine bleach and water.
I have a [pool filter] sand substrate, no rooted plants yet, but a good mass of floating Aanacharis. I've been doing a 10g weekly water change (about to drop to 5g) and maintain tank nitrates of 5ppm. (I have very high nitrates in my source well water so have to pre-filter to remove).
I also go back to the 60's and 70's when I suffered from multiple tank syndrome. However, since I'm just a kid about to turn 59, I'm glad I'm not an ole fuddy-duddy like you and Byron!!!