Just a few thoughts from me, if you don't mind.
I think there are a couple of things you need to discover before you send this wedding, ( and the resulting profits, and the long term residual sales, and reputation building opportunities, ) to someone else.
First, you need to know who is paying the bill, and then what their budget is.
For example, if the mother is paying, then does she have absolute decision making authority, or are you still obligated to abide by the bride's wishes? Then, what exactly is mom's budget?
Then, assuming it's up to mom, you can have her see the size of the finished bouquet, by having her hold a 5" orb, as suggested previously. ( And by the way, if you really do not want to make the bride and bridesmaids shell bouquets, you can easily suggest she get them online from etsy, and still volunteer to take care of the rest of the order. Never be ashamed to admit that a colleague has more experience in one area than you.)
If it is the bride's wedding, and her decision, then you need to talk to the bride before you go any further. I can't tell you haw many times I have been sucked into dealing with a third party, only to find out after hours of worry, that they really were not representing the bride accurately.
Then, assuming the bride is paying, you can enter into budget discussions with her before going any further.
Then, the same applies for the bouquets.
Re: the fish centerpeices...I am also not a fan, but it is not my wedding, nor is it yours, and these cp sound easy enough to create... and can be very profitable. I agree that the fighting fish are a better choice than the gold fish for stated reasons. (We "flower people" are pretty spoiled for choice, and it is easy for us to think that we are so much smarter when it comes to tasteful choices, but Martha Stewart and Jeff Lathem are both a lot richer than me, so WTFDIK?)
Re: the tiki torches... I do not do artificial flowers, so I would offer a fresh flower and foliage alternative, because the price can usually be the same, and they can be designed in a heart beat, and can also be a great profitable item. I've done lots of them that have turned out really nice, very pretty, and very tasteful.
Re: the leis to decorate the tables, they can be purchased ready made, in various sizes, so that is the least of your worries.
All in all, I don't think this sounds like a project out of your ability...you have shown your determination to succeed, and you definately have the talent to make it work. Most of it can be done days, or even more in advance, and stored in your cooler.
Sometimes just the fact that it is new to you, and big, and different, it can be scary, but when you break it down, it's not really that big of a deal.
If you need help on how to do it, PM me, and I'll walk you through it.
So, long and short...before you pass on this, find out what it is you are passing on.
Then, after knowing what you stand to lose, or stand to gain, then and only then, you can decide if you want to move forward with this wedding.
Oh, and no need to feel funny about saying "No Thanks", ...service providers do it all the time!
Tent companies often give up jobs to other tent companies, as do linen companies, event venues, live music bands, etc.
All you need to say is " I am so honoured that you thought about us for your wedding, but this type of work is a style that we do not normally create, and I don't want you to be disappointed. May I recommend a few colleagues that provide this style of decor? I am sure that you will find their work to be more in line with your vision."
Good luck with your decision.
Joanne