I grow landrace sativas indoors fairly regularly, its kind of a 'thing' of mine, and there's a fairly simple secret. Don't flower your seed plants. Keep them in veg forever. Instead, when they are old enough to sex from their preflowers, cut your female clones, and when they have sufficiently rooted, put them straight into flowering. Many tropic zone sativas will grow vegetatively for three-five weeks after 12/12 induction, ending up with an overall 4-5x stretch, and flowering them when they are clones of 12 inches or less will still result in some big, healthy plants without the adverse growth problems that can be caused by 12/12 induction before the plant is sexually mature. (See some of hazey grapes grows for visual representations of these effects)
Also, yes, they will often herm like a motherfucker, partivularly thai dominant strains, late in flowering for either no reason or the slightest provocation. Just have to stay on top of it, which ain't easy.