Hi
You are truly spoilt for choice in your part of the world check out the following site:
Wye and Usk Foundation
This is a passport scheme which provides either bookable Beats ie main Wye and Usk Stretches or Roving Vouchers on the smaller tributaries.
Once you sign up you will get a Passport brochure giving all the details (Details also available Online)
As your new to Fly Fishing I would reccommend the Roving Vouchers as generally the fishing is easier on the smaller streams and cheaper, plus you don't need big casts, make sure you have a selection of the following flies for the smaller streams:
Diawl Bachs
Black Gnat Dry Fly
Parachute Adams
Adams Dry Fly
Klinkhammers
Gold Head Nymphs (various)
I'm sure others will reccommend extra flies on here but these are a good start.
You'll need not much more than a 5wt rod with a floating Line
Beyond that some floatant (Gink is Good) sinkant for your leader tip and Polarised Glasses.
One other tip is to use a single length standard Mono Line Max 5lb b.s. for your leader, as a beginner you might get alot of break offs in trees etc and this is by far the cheaper alternative and I've caught enough small stream trout this way to know it works. don't worry too much about multi fly rigs its more about putting a fly in the right spot.
Best of Luck
www.flytripper.co.uk