Disregarding expensive hi-tech solutions
There are really only three answers, and you've covered them in your question; with some extra choices within each one:
No on-stage tuning; no help
The only way to achieve this is with a separate guitar for each tuning.
No on-stage tuning; a helper
While you're playing, the helper is preparing your guitar for the next song. Obviously this requires at least two guitars.
If the tunings require different strings, you'll want a different guitar for each string set; it does not make sense to have someone re-stringing guitars during your set! Logic says you could do your set in any order if you had two guitars in each string configuration (so you can play one while your tech tunes the other), but if you plan your set around it you could probably get away with fewer.
Simply (!) practice retuning so that you can do it quickly. Avoid guitars that make this difficult, such as those with a floating bridge. For example, anyone with a decent ear should be able to retune from standard tuning to drop-D in a couple of seconds, without a tuner.
As with the off-stage tuning situation, you will need at least one guitar in each string configuration.
Only you know what set of tunings you're using, but you should be able to group them into families according to how much tuning it takes to go from one to another. If you have guitars to spare, take one per "tuning family" so that your set never involves retuning all six strings.
If you're amplified, run your guitar through a chromatic tuner, then to a volume pedal (or just a mute switch), then to the rest of your signal chain. That way you don't make your audience have to listen to you tuning - unless you want to make a feature of it.
Mechanical tuners, tuning wrenches etc. are useful when restringing a guitar, because there are so many turns sometimes between fitting the string and it being "almost there". For the few turns you'd be making between useful tunings on a guitar where the strings are already up to tension, I don't see any great advantage to them.