A little before he went into isolation, I saw two tiny swordtail fry swimming among the floating plants, so for their protection I put them in a breeder bin (it's fine mesh netting in a frame which hangs inside the tank). They appear to be doing well, and are no longer bait.
The shark and the remaining neon are also holding their own, as are the two plecostemi. So now the count is:
Gold gourami: 1 male
Blue Gourami: 1 lage female + 4 small probably all female (maybe one male, hard to tell at this age)
Bettas: 1 male, two large + two small females
And lots of plants, both natural and plastic. The bulbs sprouted fine, but the leaves started to rot almost as soon as they grew out. I've added some aquarium fertilizer to the water, we'll see if that helps. They have plenty of light, both from the tank and indirect sunlight from the window.
I think I'll leave off buying any more fish. Not sure how long this hobby will last.