When sailing a ketch under full sail and the wind strengthens and you need to reduce sail, do you
drop the mainsail before the mizzen, or vice versa ?.

I solo sail a fair bit , when the wind comes up I drop the main completely . At night , reefed main just in case, no mizzen. I loose to much boat speed unless it's at least 15 knots of wind just running the mizzen.

When I sailed a ketch, I eventually didn't even have reefing lines on the main. First reef, drop the main completely. Second reef, get the big headsail down. Third reef, actually put a reef in the mizzen. That left me with small inner jib and small mizzen, really balanced and comfortable.

Some ketches will not come about with no mizzen up.

You can bear off to get the speed up and then go for the tack but they will just stall before going through the eye of the wind.

So what's the advantage of a ketch rig on a smaller boat like mine. My Santana is a sloop but I seem to remember H G's H 28 was a ketch, is the ability to have a greater sail arrangement important on a 28 footer or is the extra mast just more work ?.

My family experienced the joys of a keelboat on a H28 when learning to sail.
IMO the ketch has smaller low aspect sails which are/were easier to handle than a sloop rig for the same volume of sail although these days with furlers ,lazyjacks etc. not so much.

Sam the ketch is all about options, as to reefing at least in my case with the wind abaft of beam the mizzen would be taken in or scandalised, if the wind was fwd of beam I might roll some of the head sail up or reef the main. I predominantly use the mizzen to balance the sail trim, with the jib & main trimmed to best effect I trim the mizzen to create minimal weather helm, to tack I have the mizzen tight hauled as possible and the jib partly furled, it's a juggling act , gybeing on the other hand is a piece of cake ( if you aren't using or remember the running back stays )

Sam it's so you can run two Spinnakers and get into twice as much trouble . I have only put up a mizzen Spinnaker on mine .