First off, I think you can do better than $54,000, and is that including the $9,600 for the generator? I also think you can do far better on this.
Does this price include a fire suppression system? If not, add $3-4,000 This is something that you will want/need if you plan on using any appliance past an oven.
It may/not be required in your town but will be in another, limiting where you can work.
I'm interested in why you would want a 12' serving window?
A counter top oven is going to limit your capacity to produce your key menu item, baked potatoes.
If I remember correctly(been a few years since I made bakers in a restaurant) you can place approx 30, 90ct potatoes on a full sized sheet pan, so a counter top oven is only going to allow 2 maybe 3 half sheet pans (30-45) at a time.
A full size oven will allow 3 full sheet pans allowing you to cook 90 spuds at a time, with a cooking time of approx one hr.
You can buy a 36" flat top grill over oven and have that in one place under the hood, freeing up counter space.
A warming drawer will hot hold potatoes for a short time, it is best to serve them within 30 min or so, the flesh will turn from fluffy & white to pasty and will start to turn brown on you, no one wants an old potato.
Hot dogs????? Everyone does dogs, you might not be able to serve them some places, or have five other vendors selling them also.
Are you going to be staffed with skilled cooks, or just worker bees? If you have skilled cooks, then I would look at expanding your menu beyond potatoes.
Have you thought about char grilled burgers & hand cut fries? I'm talking a fully dressed burger, not just a frozen patty on a crappy bun with some mayo smeared on it.
You can get $6 all day for a 1/4lb cheese burger and another $3 for an order of hand cut fries, that's $9 a wack, vs???? (how much are you proposing for a potato)... I wouldn't pay more than $5 and would rather see it for less.
That $9 burger and fries cost me $1.90 to produce with a $7.10 profit, how much profit will you have on a baked potato?
Fresh lemonade shake ups do well, and have a high profit margin, there are several threads on here about fresh lemonade.
I wouldn't waste a bunch of money on a pos system, you can buy a nice cash register that will give you all the reports you will need for under $300
I would like to see a layout of the trailer you have been given bids on, along with what you get for your $$
Also, what will you pull the trailer with?