I think the best way to promote is to announce, but not to make any assumptions about whether yours, or a competing sub of the same topic, is the one that is to take off with popularity.
I think subs of similar topics should merge until communities get large enough to desire a topical split.
Amazing! I have nothing but good experiences from Jemca (yes, the very same one in Colindale).
I found their service prices high, but I feel like they always did a good job and they were pleasant to work with. I also found mostly good prices with their Lexus parts desk.