1) What type of soil/substrate should I use/

Hard to say. Two basic schools of thought when it comes to "bogs". A "true" bog which is a kind of attempt to recreate a natural ecosystem, low nutirent, acidic, carnivorous plants, orchids etc, this stuff likes a 50/50 sand/peat mix. Or a high nutrient bog that is for things like marginals, gentians, iris, skunk cabbage, sweet flag grown in high organic content muck. Best to kinda figure out what you want to grow before deciding what conditions you need. Find a swamp or bog ecosystem and figure out what grows there.

2) Can the container be above ground?

Sure. Some people even have indoor bogs. Above ground containers are going to be more susceptable to freeze/thaw cycles but in zone 7/8 that shouldn't matter too much again, depending on what you are growing.

3) Where can I find a list of sources for the plants?

Not sure there is a comprehensive list anywhere. For 'true" bogs you can try places like Cook's, Northwest, Wild Orchid Company for things like CPs and Calopogon, Pogonia, etc.

But I think you really wanna figure out what type of bog you want first. Do you have full sun? Decide which plants you want to grow then it becomes easier to track down the conditions they need as well as the plants themselves.

Here's a link for plants that do well in very moist soil, or with a few inches of water. I grow all my plants in containers...easy to to care for, just water. I enjoy the plants as they grow so quickly in one season I can have a jungle-tropical effect with Canna/Taro/Thalia or just a tiny watergarden of miniature plants in a small shallow bowl...lots of fun to play around. (Click on each plant for more info). josh

Here is a link that might be useful: Marginal Plants

Here's one source I've used for info and plants. Also Plant Delights has unusual often variegated Acorus, Carex, Colocasia, Canna, etc. josh

Here is a link that might be useful: Lilypons