Dapol https://www.dapol.co.uk/shop/n-gauge/diesel-locomotives-n-gauge and Graham Farish (Bachmann/Kader) http://www.bachmann.co.uk/prod1.php?prod_selected=farish&prod=3 are the two main suppliers/manufacturers of British rtr.
The Dapol Class 33 would just about pass for a Metrovick from a distance (the old Lima OO/HO Metrovick were re-painted Class 33s. The Dapol BR MK3 and Farish BR MK2 coaches would be close enough for the Irish stock of the 80s onwards.
The main draw back would be trying to achieve a decent paint finish on the locos and coaches together with spoiling some rather nice models and destroying the re-sale value.
Probably better to stick to Japanese or try out American N gauge
If you placed a DC loco (without a decoder) on a DC layout as you say above, the fact that there is another loco on the same powered track would NOT cause damage to either. If there was power to the track both locos should have moved.
On the other hand If you placed a DC loco (i.e. without a decoder) on a DCC layout that was powered up, the motor would have hummed and buzzed and there is a slight risk of damage if left there for more than a few seconds. Putting a loco with a DCC decoder on a DC layout should be perfectly safe for the loco, it just won't drive unless the decoder's CV 29 settings have enabled DC mode.
Hope this helps
Good to see that there IS interest out there. No wonder 21mm looks better than 4'1...
For anyone doing 7mm scale, it really is no more difficult than 32mm gauge. Loco axle available, wagon/coach axles easily adaptable, C&L bullhead track only needs a 36.75mm gauge. Plus there are plenty of kits available too.
With all the high quality RTR out there, it is no surprise folk stick with what they know, but there is even more satisfaction to be had in doing your own thing and being different. Well, I would say that, wouldn't I?