I believe you can buy chocolate flavouring oil, but I haven't used it, so I can't tell you too much about it. White chocolate flavour goes pretty well with most things though, so it should be fine either way.
In very hot, humid weather, you need to use substantially less cream, rather than slightly less. More like a 3:1 or more for dark chocolate, and 4:1 for white.
What do you mean by they haven't set hard? Is the ganache dripping off the cakes, or they make an indent when you touch them? If it's the latter, it might be OK, but if it's the former, I'd scrape the ganache off and try again.
Are all the photos yours? There seems to be a huge difference in the professionalism of some of the photos as opposed to others.
Facebook doesn't share business posts with everyone who has liked their page, so your posts mightn't be even getting to everyone. A website is an absolute must from a customer point of view.
A 12 inch mudcake is a bit different - I find them pretty impossible to get a knife through if they're not pretty much defrosted, and that does take a few hours. But OP, the night before will be fine - if you want to take it out 2 days before, that will also be fine.
I've had mudcake on my bench for two weeks and it's been fine. But, I don't know if I'd risk quite that length of time without freezing to give to customers. I'm sure it would be fine, but not sure enough to recommend it.
How's that for confusing?
I like them better and find them easier to handle when they've been frozen, so I always try to do that anyway.