A thumbs up for Leathergraft from me as well. They are not expensive but are very good quality and very easy to deal with (they even made a shorter length ladder section for me for only a few extra quid).
Maybe this will do it:
The arrows move left and right on the beat.
The led's flash.
There is a sound beat which can change to a voice that counts (in chinese if he is really struggling).
There is a volume control with headphone ouput (which I am sure would connect to the aux input of a 500w amp and cab just for getting the point over).
Another Greatest Hits Radio listener here. I moved to them from Radio 2 a couple of years ago and although the content is only 70/80/90's some gems from these era's come out of the woodwork occaisionally. They also the odd special which can be entertaining.
One of the big advantages is they took on most of the best dj's from Radio 2 so Ken Bruce's Pop Master is always on the listening list.
It was the Mic Mechanic Phil simple to use and a wide range off effects on offer with each parameter having it's own control knob. Another two to look at would be The Duplicator and Harmony singer. These are still available and reasonably cheap on the secod hand market. They have a Voicetone range which is a newer line with similar features i.e. the D1 has doubling and detune as it's features.
Another thumbs up for WhatsApp, keeps us up to date and then one of us transfers any date information into the band diary (old school paper version) and we discuss any events at rehearsal.
This is easier than hearding cats for most situations😊
Our vocalist used the TC Helicon reverb unit (foot pedal version) to good effect so their current range would be worth a look as per Mykesbass post above.
Expanding on Ped's headphone amp/output suggestion how about going for a 500w class eadg, beadg for 5 string, pre/power amp fed from an 18v dc passive/active pickup system (plus all the additional media suggestions put forward).