The thing that kills startups at some level, is the founders giving up.
One thing I tell startups all the time is that the best way to grow is to make their product better.
I think the best thing you can do is be aware that as a first time founder you are likely to be a very bad manager.
The company just needs to see you as like this maniacal execution machine.
One thing that often disrupts momentum and really shouldn't is competitors.
Even though plans themselves are worthless, the exercise of planning is very valuable and totally missing in most startups today.