Citrus seeds should not dry out. They may sprout when dry, but the germination rate would be ~20% at best.
I don't know about bonsai for citrus, but they tend to have a shallow, spreading and fibrous root system, so keeping them in pots is not difficult at all. Because of the fine root system, they should be in something light that drains fairly quickly.
I spouted some tangelo seeds, which have struggled. My lemon seedlings however have done well, with slow but steady growth. I'm trying kumquat seeds now. The germination rate varied quite a bit - some of the tangelos only took 2 weeks; the lemons took more than a month.
Two things to look out for with citrus - they are succeptible to root rot if over watered. And I would suggest keeping them away from any nightshade type plants (peppers, tomatoes, eggplants, etc) - those plants can be magnets for mites and aphids, and while citrus won't attract those pests, they are sensitive to them. Seed-grown citrus can also take a long time to fruit - anywhere from 3-4 years (calamondin, kumquats) to more than 10 (grapefruits and pumellos). They LOVE light.
Lemons, limes and citrons can't take a freeze. Oranges, grapefruit and pummelos can take a few degrees below freezing for short periods of time. Some mandarins - satsumas in particular - can take temps into the mid-20s for a short spell, once the plant is mature. Kumquats and a handful of rare citrus can take temps down to the upper teens.
I have also sprouted guavas. They had a hard time kicking off the seed coat, which is very hard, so I think I should have soaked them first. They had a long, variable germination rate - I planted the seeds in September, and 3 weeks later I had 3 sprouts. A month later I had 3 more. As of this week, there are two more starting to show themselves. So I think the seeds have a long period of viability, and they will sprout when they are good and ready.
I don't know much about their bonsai possibilities, but it's my understanding that they are shrubby, can be kept small, and are somewhat vigorous. They can't take a freeze. In tropical environments, some varieties have a reputation for spreading and becoming weedy, and once established they have a reputation for durability. The flowers are apparently quite attractive.