My plan (is) to set it up much like a reef tank with a bulkhead in the bottom and a sump under the enclosure for the water to drain into. The sump will have an easily accessible pump
In my opinion, based on about 8 water feature builds of varying size, complexity, and failure/disappointment history, this is hands-down the best way to do it. Bulkhead, gravity sump, return pump. The return pump can be a canister filter, you can even slap in a UV sterilizer after the filter if that turns your crank. Or you can just have a trickle filter atop the sump, and some baffles & charcoal to "remove the big pieces and the odors & colors". I like media bags and a plain old pump if I've just got a little dribble going (the media & the plants remove enough of the yuck), and a canister filter if it's a real stream (for various reasons I have drifted away from these, over time dialing back the flows in my lively streams to where now they mainly just dribble gently).
But whatever your filtering & pumping details are, the key is to get all that water-quality infrastructure outside the viv.
Because the real key is to have easy maintenance, because if it isn't easy you aren't likely to do it.
And an unmaintained water feature is going to get nasty eventually.
Good luck, have fun!