There's no point using the old rims if you want to change the hubs. The original 7 speed wheelset is single layer. If possible, get double layered rims. If price is a factor, you can get the WTB 20 inch wheelset which is around 300 bucks only. I don't know if it is still in the market though. The non QR hubs can be converted to QRs. The shaft used in the non QR are solid but hollow ones can be found in most local bike shops. The shafts are cheap and the rear ones needs no further modifications, just dismantle the original and transfer the components on the new hollow shaft but the front ones needs to be sawn off though as Dahons are only 73 mm wide and most front shafts are 100 mm. Another problem is......... I don't know if you can find 73 mm QRs.

PM me if you want an 8,9 or 10 speed wheelset. I am thinking of changing mine anyway. That is , if you are interested lah! 

Ok, bicycle term 101.
Rim, the round thing where the tire is attached to.
Wheelset = Rim + spoke + hub.

Kimbell Jaya do stock them but I am not sure now.

Almost every bicycle shop I walked in sells rim. Which type only. Meaning expensive or affordable type. Just walk in and ask.
The last I heard, labour for lacing wheel is 2.50 per spoke. Excluding materials. The price goes up exponentially wih lesser spokes.