The first place I ever interviewed with was McDonalds but it was one of those things where they interview around ten people during that day.
The first job I got was as a cashier at Hobby Lobby, of all places. I had relatives that worked there for years and when one left for another job, I was recommend and later hired.
Im sure the manager knew but I never had any trouble. There were actually a couple of people who knew, well... After three months I had to leave suddenly due to emergency health issues and apparently one of the girls working there started a rumor that I was getting a sex change and joked about it, but she was confronted by one worker who looked after me confronted her about it even though I had quite a week prior and the girl actually began to cry once she realized what she was doing.
I don't like Hobby Lobby but it was a job and an experience. It did get old after a while, these ladies stopped in while on a road trip for a convention and while checking out she leaned over the counter and whispered in my face, "You know that God is our lord and savorer, don't you?"
For formal occasions such as an interview I wear black jeans that were not too tight nor too loose or even a pair of gray jeans that look like slacks, and a nice button up shirt or a polo and a pair of black chucks.
It depends on the employer. A suite would be a bit much. Someone at some point told me that wearing something similar to what the employ attire is not a bad choice. Such as hobby lobby is brown/tan pants and a blue shirt.
As for the employer and being transgender and transitioning it depends on their judgment, but mostly if they see you as a good candidate is what is important. I have met people who's manager was supportive of employes who are transitioning, especially when it comes to paper work and legal name and gender. Places that are a large corporation such as target, Walmart, Meijer, are not a stickler to who they hire.
If you walk into a hobby lobby you will notice that all the employes are well groomed and well mannered, for the most part. There girls were allowed to have earrings but men were not allowed to.