I'm about to flush the echo's coolant. Is there anything missing in this checklist?
Checklists are good, but I have a question: "Why?"
Navy used to do certain maintenance items at certain periodicities because the manufacturer determined that it was "good engineering practice". However it's expensive ("good for the engineer's practice"), and frequently the collateral damage (time, labor, difficulty getting things apart/together, disruption to operations, realignment/recalibration) was more costly than the potential pitfalls of
not doing the maintenance.
Later the Navy philosophy shifted to "performance monitoring". Run the equipment, do a bunch of testing, and decide whether something needs maintenance. Usually the decision was to keep on monitoring.
In the case of flushing coolant, draining the fluid introduces air to a system which is supposed to contain fluid. At some point you're going to have to get the air back out. Until the air is all gone you're risking the effects of accelerated corrosion and acidification of the system's piping & debris. You're also disturbing whatever is now harmlessly sitting at the bottom of a piping loop, risking the possibility of breaking it free to go jam another run of piping or grind into the water pump's bearings/seals. And last but not least, you're loosening bolts & drains that (so far) aren't leaking.
Instead of doing maintenance by the calendar or the odometer, what about just keeping the radiator's expansion tank topped off with antifreeze? Or sending a coolant sample for lab analysis, and then doing a feed&bleed (instead of adding air bubbles) as necessary to reduce the concentration of whatever's out of spec?
If deferring maintenance just doesn't feel right, then at least do the maintenance the way the manufacturer intended it to be done: pay an auto mechanic to do it so that that you can help them support their family.