Use 1762 for the Rochefort. The best sources I've found say that 1762 most likely originated from Rochefort, and it is delicious.
3787 is probably my favourite yeast. It'll do great in your Belgian Abbey beer. It's used by two of the remaining Trappist breweries. It is incredibly tasty.
Make starters and aerate really really well. These are big beers.
Keep the Nottingham. Sometime you'll have an infected starter or a stuck fermentation, and you'll be glad it's around.