Does the vow include giving away half the profit from a second project, or is it limited to the first project only? And does the vow apply to a project where the questioner brings in the client and partners with his friend, and are expenses deducted before giving away half?

If the vow is merely an intention, it is not binding, and nothing is required. However, if you uttered it, then you have fulfilled it, praise be to Allah, because your statement: "If this project did not have an effect" is specific to this project only. Consequently, your involvement in other projects does not obligate you to anything, unless you intended to donate half the profit of every project that comes to you in that year. In this case, you are obligated to donate.