The turkey fryer is a ok option if you are looking for capacity. FYI, you will be in violation of health dept regulation by using it. Will you get caught? Probably not but in violation none the less. Everything is supposed to be cook and prepared off the cart when it comes to serving hot dogs for a paid event. This means no crock pots, self serve condiment, extra cookers for capacity, etc. NC rules state that a push cart can not be used for self service. This includes pre fixed hot dogs (dog in bun) in warming trays, condiment stations, etc. that a person would pick up and do them self. You have to fix each order and hand them the dog.
With that said, you are brand new at this and probably should not have “jumped in” to a job this large to start. This type event is tough on any cart much less a small capacity one and with someone brand new. I would rather hold off bidding something like this rather than make a bad impression. When people have to wait any length for food they dont like it. Even with my experience I would think twice about doing this type of job. I have feed a crowd over 1000 at my bar setup but they just come and go as they were hungry through out a 5 hour period. Feeding 400 at once where they are expecting to all eat at a certain time is tough off a hot dog cart of any size. If it is going to be a all day event with people eating at different times as the day passes then that would not be to bad to pull off with enough help and staying on top of keeping dogs cooked, condiments filled, etc.
I am not giving you a hard time I would just hate to see it go bad and people not be happy with you and your services. Good word travels slow but bad travels like wild fire. I would hate to know I had 400 plus people that could possibly talk bad about my services.
If you do decide to do this hire plenty of help and do some “hands on” dry runs with that help to make sure they know what and how to do.
Good luck and let us know what you decide and how it goes……