OK, let's just dive right in since I am well along the way and a bit ahead of you (having already purchased many from Andy)
Let's talk about the terrarium first then the plants you'll need rather than other way around. The basic setup with waterfalls, etc. sounds fine. There will be lots of humidity if the top is closed. So you'd better get a small fan to move air somehow. For mine I opted to run a hole in the top section which is acrylic. Use ONLY 12 volt fans - even though there are lots of 110V models out there, they'll short out with the humidity. I purchased 4 of these
Coralife 3-1/8" Cooling Fan Kit I use one inside tanks and one outside (more on that in a bit). The inside one is running 24/7 and helps dry off all the plants between mistings. You could just place fan in an opening in lid (or have a new acrylic lid cut along with the hole and mounting holes.) That should keep everything nice and breezy inside.
Misting: This is up to you. Misting by itself MAY NOT keep certain plants wet enough and in some cases may keep the plants too wet (especially ones in sphagnum in pots or baskets). Andy's Harealla's mounted on sticks will do just fine with heavy misting as long as roots don't dry out too much. My MistKing system runs with RO water using an interval timer set to run 8 seconds every two hours and this runs through another timer where I control length of day/night. So far every plant in the mist path stays moist to wet during day and dries out a bit at night when misters aren't running.
As to types of lighting, my tank is 30" from top to bottom and I use a bank of 4ea 48" T5 strip lights in individual reflectors. Therefore the external fan - I need to blow the heat away from under lights. This fan stays on during the "day" and off at "night". The T5s run WAY cooler than HID but are still warm. My light meter says between 500 and 600 FC about 1 foot away. This is as I expected starting with 2000FCs. My new tank will only be 24" high but much wider and I will be running a bank of 8 lamps and 4000FCs. There are lots of Compact Flourenscent fixtures (CF for short) and individual bulbs. You can even make your own fixture by retrofiting the top of your extisting tank (the hood). My favorite spot for the least expensive CF lights is
Full Spectrum Lighting and Light Therapy I have about 15 of their lamps. By the way CF units are MUCH more expensive than straight tube fixtures, but probably fir the shape you plan better. This one -->
55w Compact Fluorescent Lamp puts out 3500 lumens or about 350FCs and you would need several to get 500FCs at the bottom of your tank. There's also -->
Hydrofarm - Hydrofarm FLC125D 125 W Compact Fluorescent Bulb - Daylight - New Low Price I am not sure of the light out put of these units.
Now for the plants. It may be difficult finding enough seperate spp from the same area to satisfy your requirements if you plan to mist or grow under lights. Andy's watering requirements can be taken with a grain of salt with terrariums. When he says 3-5 waterings per week and keep moist in same combination, I would change that to daily watering and frequent mist/high humidity. For instance I purchase two different Cischweinfia which said keep moist/water 3-5 times per week. Even with daily dunkings (soaking) and frequent misting, they started dying off and refused to flower. They set buds, but the buds dried up. I moved them to terrarium in same baskets and water them maybe once a week (if that) but subject them to misting ever two hours and they are growing well. It's really hard to read the list he posts and make any defenite plans. Give them and call - you'll end up talking to Harry, his brother. Explain in detail your setup and let them be the judge. If you e-mail them, don't expect a speedy reply - sometimes it's weeks.
Lastly, will high humidity alone be enough for your plants? I doubt it. Even with all the mist and humidity I provide, there are drier sections of any terrarium (thankfully) where you may choose to grow a dendro or maxillaria that cannot tolerate wet feet. They'll still need to be watered somehow. If there are any other specific questions regarding your project, feel free to PM me and we can discuss.