TC - The biggest problem you have is that most "trees" need full sun. If I were you I would look for a houseplant that looks like a tree. Doing research on which houseplants will do well in your light conditions, if your terrarium has a plant light that will help. I have a "frog" terrarium and often put live plants in there for him to dig in. A tropical ficus, one with a swollen base would look cool for an "avatar tree" (I've seen these at home depot), but you will definately need to keep it near a window or have a plant light for it. You could even put some "baby tears" or "dichondra" around it, how about some mini ferns?
Sounds like a fun project . . . good luck!

I making a terrarium for just plants (although I am using and exo terra which is usually used for animals) and I am putting a grow light in it to help with plants. I had considered using a mini orchid as a center but I have heard they are very picky plants.

I really like you idea of the tropical ficus. I found a few pictures of ficus bonsai trees from a contest and I have a few questions.

http://www.artofbonsai.org/contests/wbc_2009_photo_contest/entries/pedro_morales_ficus_benjamina.jpg

This one appears to have vines and I am wondering how that is done. I read something about grafting and I am wondering if that has something to do with it?

http://www.artofbonsai.org/contests/wbc_2009_photo_contest/entries/nacho_pitecellobium_tortum.jpg

In this one the judges keep referring to carving and although I think I know what they are talking about I don't completely understand. Is it just the texture or can you actually carve/split the tree to give it the texture you want?

Is there a website or book that might have good information on grafting and carving?

You also mentioned a maple tree, but those need to live outdoors (including a cold dormancy period in winter) for life. Completely unsuitable for a terrarium. Do some basic research before trying live trees in there. Your comments about splitting trees to achieve 'texture' and about "vines" or grafting, suggest that you are an absolute newbie when it comes to bonsai or possibly even growing anything, and I think you have quite a way to go before considering doing a terrarium for any trees. Just keeping them alive for a week requires knowledge and experience, and you can't treat them like house or aquatic plants without a lot of learning. Maybe find a local bonsai club to join and start at the beginning. Very few trees of any kind will do well in a terrarium anyway and first just learning something about trees, never mind bonsai, would be a good place to start.

Tropicals are really the only trees you will have luck with growing in aquariums. Click on my link to see how I have grown tropicals in aquariums.

Here is a link that might be useful: Bonsai in Aquariums

And when I say aquariums, I really mean terrariums. They are basically the same thing.

I totally admit to being a noob, which is why I am asking around to a bunch of different places. There is a bonsai club in my area which I have sent a message to regarding meetings and joining.

I haven't actually gotten my terrarium yet but I know which one I want. I am actually in the research and architectural phase. I am working on some basic drawings and notes on what all I need and where I want everything to be. I figure when I get my terrarium I will spend 2-3 months putting together the non plant parts. I want to put in a small pond and water fall in one corner and I know that there needs be good air flow to avoid mold growth and for the plants. After I have that all set up to my liking I was considering putting a few plants and keeping them in the pots just to make sure I can keep them alive and slowly work my way up. I figure in 6 months or so I might tree keeping a little non tropical bonsai tree alive outside of the terrarium and see how that goes and maybe in a year to year and a half I can get a bonsai tree for my terrarium. I figured if I can pick the tree or plant for my center first then I can pick plants with like needs around that.

I understand that some plants/trees require a dormancy period which is why I figured I would need a tropical plant/tree. Since I don't know a lot about growing things let alone the art of bonsai, which why I seek the vast knowledge of the experts.

On a side note... That link you posted Ryan was very helpful. Although it started a hole new search into the topic of "What is an aerial root and why do I want one?" .... I will get there eventually...