You've asked a mouthful there but I certainly respect your attention to detail and the fact that you've done some serious downrigging "homework"!
I agree with all the Cannon Downrigger advantages you've identified and let me address your concerns one by one:"No tilt up feature, which is how I'm used to retrieving..."
I utilize a Cannon Weight Retriever https://www.sportco.com/store/pc/Cannon-Downrigger-Retro-Ease-Weight-Retriever-2250122-756p62032.htm
The Weight Retriever allows you to swing the ball to the base of the rigger and lock it there with one hand. It's also a great way to keep the ball out of the way when you have a fish on. The tilt-up feature is no help when you and your fishing partner are trying to net your fish! "When blackmouth fishing, I'm accustomed to slowing down the descent until the weight "ticks" the bottom. However, with the power down feature on Cannons, I'm concerned I might end up with some pretty severe backlash...."
Cannon and Minn Kota are part of the Johnson Outdoors Company. As the undisputed leader in underwater electric motors, Minn Kota brought a lot to the Cannon "party", namely a variable-speed motor. Most downriggers have an "ON/OFF" motor but Cannons cycle through FIVE SPEEDS from crawling to SMOKIN'
In other words, when you hit "ON" the motor starts off slowly and then automatically advances to the fastest speed. when the auto-stop kicks in, the motor cycles down very smoothly so as to minimize jerking which could lead to the aforementioned and dreaded backlash.
Powering down is the best way to use a Cannon and they will tick bottom and allow you to bring in a bit of wire easily, consistently, confidently and smoothly."-What can I do for maintenance on the Cannons?"
In my opinion developed in nearly 15 years of using Cannons, they are lower maintenance than any other 'rigger that I've used and I've used 'em all.
I hit the power connections with Corrosion Block at least a couple times a year and WD-40 the boom roller. In addition, I replace the wire every year and I exclusively use Cannon Terminators https://www.sportco.com/store/pc/Cannon-Downrigger-Terminator-Kit-756p62033.htm
The Cannon Terminators last FAR LONGER than those wire-damaging crimps. In fact, I've had Terminators last an ENTIRE season which in my boat is well over 100 fishing days.
For the original purchaser's lifetime, Cannon's Warranty covers: The boom, motor, and reels, plus all plastic parts, including but not limited to frames and bases, will be free from defects in materials and workmanship, subject to normal wear and tear.
You'll not be disapointed with Cannon's and with their built in Positive Ion Control (PIC) voltage control, you can forget about a Black Box as well!