I have a startup with 2 co-founders (me and my partner). My partner is a programmer, whereas I am a half-programmer, half-designer, half-business guy.
I have had exceptional experience with pair programming (with others), and I wonder if we both should pair program at the early stage of web development, or we are better of splitting the work so that the development can be rapid.
I am worried that pair-programming at an early stage might slow things down.
With pair programming you may find that "what" gets programmed will be far better than how much. Your communication is going to increase because you won't have to stop and either document in too much detail (not that they shouldn't get documented) what you've done or hold meetings.
Be prepared to hit some points in the process where you have identified a complex part of the application and you need to let the programmer work on it alone.
As the part-time programmer, you're going to have a better understanding of the application and should be able to help with debugging and be able to handle more than just first-level service calls. I'm more interested on how a company handles my problems to see if I want to use their site for the long term. Something always goes wrong; taking care of it is what separates the good from the bad firm.
Pair programming will increase your initial development time but should increase code quality. That should reduce support time and make it easier to extend later. It will also mean that you as only half programmer (you seem to be 1.5 people by the way) will still have full knowledge of the the code base.
Well worth spending the extra time at this stage.