Although, as you say, Cardiff do not allow instrument training these days, I can give you some historical information.
I have entered the hold at Cardiff as high as FL80 and as low as Altitude 3,500. Generally FL60.
Although you're right that it would be nice to be level at platform altitude before the base turn, it rarely happens at Cardiff or elsewhere for that matter.
Here are some things you can do to help with this. Set the correct power and trim for a rate of descent of say 800'/1000', take a 60 degree intercept inbound to get established early, get as much as you can done outbound (checks, idents, get go round intructions<generally straight ahead altitude 2,500 ft at Cardiff>etc.). Cardiff ATC are (or at least were) pretty good at offering you an extension of the outbound leg if they have kept you high at the start of the approach. If they don't and you perceive you have a problem with losing altitude, ask for an extension outbound.
As far as an off airfield NDB is concerned, the base turn complete call still applies and there is no need for further R/T when you go over the beacon again inbound unless requested by ATC.
Good luck
Nasib