I've avoided serissa all these years because of the stories of difficulty and finickiness, and because I'm not keen on indoor lighting set-ups and such. Then, a thread here at B'Nut started by Will a few months ago started me re-evaluating them, and shortly thereafter I saw one with the sort of wild Chinese style nebari/exposed-root that appeals to my strange tastes. So three weekends ago I stopped by to see Robert Cho at Asia Pacific Gardening in Kent, WA, and among other things I went around looking at his serissa, which he imports by the thousands from China for the mallsai side of his business. I wanted to get one, so I did, one of his larger and least "mallsai" ones, but not until I had picked his brain about them. Here's what I recall of what he told me, which, since you're already very knowledgable from years growing them, probably will not be of much help, but I offer it anyway.
If they flower, he recommends cutting the flowers off before they open, since they rob a great deal of vigor from the branches they appear on and can weaken them to the point of die-back at times. So your quest for flowers may not be an altogether good thing from the standpoint of the tree's overall health.
They really don't like leaves touching each other, so keep them sparsely trimmed to avoid that.
Outdoors in summer when nights no longer fall below 50F.
Partially sunny windows are fine/ideal (unless one has a greenhouse), as long as the windows are not drafty in winter. Humidity tray.
Routine care is fine - they respond well to a bit of neglect. Less is more.
I've set mine in an appropriate window, trimmed it a bit initially so that no two leaves are touching, given it recommended care and simply enjoyed it - in the three weeks I've had it, it has not had a single leaf turn yellow or fall off or look sickly. I'm very pleased with this tree, which evokes the word "Bitchin'" every time I see it! I'm a believer now, and it's such a nice bonsai just as it is that I couldn't care less whether it ever has flowers.