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Yes, and you can plant them outdoors when the weather stays consistently above 50 degrees F. in your area. They will start to sprout once it warms and they get regular water. Here is an article or two that you may find helpful: https://www.gardeningknowhow.com/ornamental/bulbs/caladium/caladium-plant-care.htm, https://www.gardeningknowhow.com/ornamental/bulbs/caladium/when-to-plant-caladium-bulbs.htm

No, CO2 is actually good for plants. They will be fine.

If they were planted outside, they likely did not survive the winter. They are only hardy to zone 10 and will die elsewhere in the winter outside. If they were brought inside for the winter, you can plant or put them back outdoors when the weather stays consistently above 50 F. They will start to sprout when they are placed somewhere that is above 50 F and they get regular water.

It really depends on the temperatures and water they are getting. Water them when the top of the soil is dry to the touch and give them a little more time. It has been a somewhat chilly spring, so they may not be as fast to sprout.

It's not too late to plant them but you may see a delay in flowering. Still, I would go ahead and get them in the ground as soon as possible. Here's an article that may also help: https://www.gardeningknowhow.com/ornamental/bulbs/caladium/when-to-plant-caladium-bulbs.htm

Once the blooms have faded, you can remove them (including the stem), though leaving them alone will not harm the plant. It will simply put more of its energy into seed production.