Well +1 to you... Congrats. If you ever do it over again, though, don't worry about a S (Federal distinction) or LLC (state distinction). Instead, just do not incorporate. Until you have revenue or investment, there's no upside to any kind of incorporation. Celebrate your enthusiasm with a party - it would be a better use of those funds. You can sign some agreement with your cofounder, but you should only work with a cofounder you're willing to trust, so even then I wouldn't be too uptight; that's me though: others who have been burned by cofounders pre-incorporation will likely tell you something different I imagine.
You can file a form with the IRS change to an S right now if you want (an S can actually be a type of C), then change back when you have investment. This is only worth doing if you anticipate not getting investment in 2015 - the upside is just that the losses you're incurring on the C will pass back to you through a K-1 and end up... back on your personal schedule C, which is (in my opinion) where everything should have been this whole time. Water under the bridge at this point - I like your combination of enthusiasm and legal compliance. Keep at it.
Anyway, same principle applies here: if you don't have an option pool, don't start creating one until you have investment. As a rule of thumb, I'd keep my legal & accounting fees to less than 10% of my expenses (ideally a lot less). If you can't afford good legal or accounting by this rule of thumb, it's an indicator you should be looking to avoid the situation entirely that requires it; don't cut corners on either and don't let their fees dominate your business' expenses.
So what's the solution? In this case, I'd sign a contract between your C corp and this developer. The contract should contain:
1) Legal assignment of all IP created to the company, including source code.
2) A non-disclosure of some kind.
3) The statement that a recommendation for an option grant of x shares will be put forward to the board *after* a minimum investment of some dollar amount has been obtained. Put a clock on this too (it can be long - 2 years for example - but something).
4) Since he's likely to balk at the idea that you're just guaranteeing presenting the recommendation rather than guaranteeing the grant (which is the correct language - only your board should grant options, and you don't want to grant them until after the investment), give an alternative cash payment in the event (and only in the event) the board rejects the recommendation; it should not be applicable in the event you fail to get the investment. If he's worried you'll get profitable without needing investment, you can put in that contingency too. Basically, pick a monthly rate... that you're unlikely to ever be in a situation to have to pay.
If he doesn't like this, point out that the options are worthless if you don't get an investment, and this protects him from any tax liability in that event. If he's worried about not naming the strike price now, offer to pay him (*after the investment* and only in the event of an investment) a lump sum of the difference between the granted option strike price and some strike price you agree on now (par value, for example) on a 1099. This will prove a modest amount.
You are correct that RSUs would be another approach here, and at least given what you told me, I'd have no issue telling the SEC that par value was absolutely the correct value (that's just me though). However, a contract that does not involve affecting the cap table prior to investment is more valuable to you both. Your goal prior to investment is to not make mistakes and not spend money. You can achieve these things by basically trying not to do anything whenever possible.
Now go forth and stop talking to lawyers, accountants, and professional consultants in general until you get some funding... And even then, at a minimum, try to follow my 10% rule. No matter what they tell you, those guys don't add value: the good ones just don't subtract it. You add value by working on your business - put all resources towards that as long as you can. Good luck.