A beardie, to be honest, wouldn't mind the full tank even as a baby and would probably love the space as long as you pack it out with things to climb on/under and some hides
thought of course if you wanted to you can put a divider in there no problem.
You'd want a 4ft x 2ft x 2ft for an adult beardie which will do them for life. A good place to start on that and someone I'd highly recommend is Volly, I just got a 6x2x2 from him for my Burm and worked out very cheap and better quality than my VivExotic ones I have :P You can get in touch with him here https://www.facebook.com/volly1?fref=ts
. Can also check the classified section for second hand ones.
Basically you're going to need a ceramic bulb holder with a 100w bulb on a dimming stat, a normal bulb will do. You'll turn this off at night time (which you can buy timers for to do it automatically) to keep a day/night cycle for your pet. You need a bulb guard over that too.
Second you'll need a UV bulb, most recommened Arcadia T5 Essex Reptile - Arcadia T5 D3 Reptile Lamp 12%
and for that you're looking for the 46"/54w one for a 4ft viv. With a controller Essex Reptile - Arcadia Ultra-Seal Controller
and of course the fittings for the bulb, you can get those on ebay
Erm other things.. obvious being decor for your viv, water bowl (though not everyone uses water bowls for beardies as not all drink from them, but get one to start off, if it's never used to scrap it and give your lizard a weekly bath as they will take it moisture that way), hides/plants, and you'll need to choose a substrate.
The best substrate in my opinion is upturned tiles. Upturned keeps their nails nicely trimmed down and they're easy to clean and look really nice. Otherwise go for play sand Buy Children's Play Sand - 15kg Bag at Argos.co.uk - Your Online Shop for Sand.
, sand is a controversial subject with beardies especially though as it can cause problems with impaction, but play sand is the safest sand if you go down that route.