I don't work for a chain or anything, but my job involves dishwashing among other things. If that's all the job involves then I can't see why any tatts or piercings will be a problem, and the larger the place is the easier the jobs tend to be (you'll just be washing up, I'm washing up, serving up deserts, waiting, cleaning and soon to get trained at putting together starters as well hopefully.) As for clothes, it's probably not worth investing in proper non-slip shoes, mine never made any difference, but you'll want something with rubbery tread ideally, floors can get pretty slippery in kitchen's especially around the sinks. A polo will be fine I think.
Do you know how you're going to get paid? If it's cash you might not need to reveal your birthname, (I don't know how things work in the states, I know that here you have to fill out a P45 for tax purposes which will need whatever name is used for that sort of stuff), and if you're being paid by cheque/bank transfer then obviously you're going to tell them a name that's going to let you get stuff paid into your account. Kimberley is a unisex name though, so you could always just tell them when it comes to getting paid/anything else they need a legal name for that legally your name is "Kimberley" but you're going through the process of getting it changed, and they only need it for whatever. You don't need to mention that you're trans as far as I can see.
And good luck, it's not a hard job or anything, it's just painfully boring. Or painful if you always forget that the hot tap pumps out water at over 70deg C (158deg F). It's a good time to just zone out and think about things though, although I can never remember what great philosophical breakthroughs I've made by the time I get out of there.
