I certainly wouldn’t snub my nose at a nightmarket laoban because some of them are making decent money, but $300k is optimistic. Selling hotdogs or whatever you would need to be open 7 days a week for 6 hours a day and sell more than 1 per minute. Walk through your local nightmarket and see how many stalls can go 10-15 minutes without a single customer. There are some successes but there are even more failures.
One of the most successful nightmarket operations I know of is a friend of the family who sells lamb at Shilin nightmarket. There are 4 or 5 staff working there now and they have an indoor area with tables and chairs that is constantly full with a queue of hungry diners. They are making a lot of money but at this kind of volume it’s backbreaking, sweaty work until 4-5am every night. I personally couldn’t be arsed.
If you are not there on time every day you will lose customers - if you visit somewhere on a recommendation and it’s closed, you probably wouldn’t bother going back.
The stalls that do best are not working with some gimmick or new idea - they are making a staple Taiwanese food, either really well with an excellent reputation and/or with a simple twist.