I have a multi payment system for clients. If one of my client projects falls over the end of the year, beginning of the next, am I able to report the full project income at its completion, or do I have to report each payment in its individual year?

[WillK]

It depends if you are cash basis accounting or accrual accounting. 

Cash basis accounting is when you report the income when you receive it: https://ttlc.intuit.com/replies/3300094

Accrual accounting is when you report the income in the year you earned it, not when you receive it: https://ttlc.intuit.com/replies/3301956