Have given up looking at rescue situations, and after discussion with Inca's breeder, have definately decided to get another Newfoundland from her. I shall be getting a male, and of course naming him Wolfgang. Then I have my two lovely Newfoundlands, with similar exercise requirements and temps, which makes life easier.
Appears she may be breeding with her other bitch in June/July this year, so by the time the litter is born and puppies ready to go to their new homes, Inca will of an age that is debatably safe enough to be de-sexed.
As TKay mentioned, it will give me the time I require to have Inca fully trained, yet she will still be a young dog when the second arrives.
I am feeling very happy with my decision. Best to start saving $$$ now, though.