Get yourself some OS Landranger maps and plot your own route on yellow and white roads and tracks. I avoided National cycle routes as some take you down some very dodgy roads with traffic.
Last year I rode a nice circuit from Abergavenny, the Gospel pass to Hay on Wye, Llandrindod Wells, Rhayader then up to Machynelth, around and back. The moutain road between Machynelth and Llanidloes is stunning. Also went west from Rhayader across the hills along a deserted track past Claerwen reservoir to Ysbyty Ystwyth round past Devil's Bridge to Cwmstwyth then on and up to Machynellth. Then north west to the coast Tywyn before coming back down toward Llandovery around Lynne Brianne and along the old Roman to Sennybridge, stunning views accross the top, deserted except for sheep, horses and hills all around, then continuing east to back across the Becon Beacons to Brecon finally picking up the Brecon and Monmouth canal to Abergavenny. Have missed out lots as I went past and through so many beautiful places. Rode up the Devil's staircase as well. There are some mother of hills going north out of Machynellth into the forests. One was the steepest road I have ever pushed a bike up. It must have been nearly 1 in 2. I had to stop every 10 feet and put a rock under the rear wheel to stop it careering off down the hill it was that steep.
Anyway a brilliant short tour. Use the national cycle routes / Sustrans where you can but in all honesty you don't need them just get some OS maps and plan your own route. This is half the adventure. The only really good NCN route I can recommend is the road between Rhayader and Llangurig. I had plotted a route along the road, but when I came to ride it discovered it was an NCN route which I thought was good of them. In contrast I have seen NCN signs directing cyclists along busy A-roads which is a FAIL imho as they are dangerous and I don't want to ride with the prospect of being killed. In fact the busiest road I rode was climbing the Gospel pass, quite a few tourists in fecking huge 4x4s occupying the whole width of the little road and refusing to pull in to let you past. It helps to have an Airzound in these narrow lanes with high hedges.
There are lots of opportunities to wild camp in Wales. There aren't quite as many mozzies as in Scotland, but you still have to be cautious otherwise you get bit.
HTH