Basically, unless you use "accrual based accounting" (which is complicated and needs an accountant to set up) then you are a cash basis business. You report income when it is actually received, and expenses when they are actually paid, even if you are paid in advance for a job. A check you receive in 2017 is 2017 income. An expense you paid on 1/1/18 is a 2018 expense, even if your subcontractor or vendor did the work in 2017.
In your case, you will have more net taxable income in 2017 and less in 2018, but it should all even out in the end.
For the gift issue, I would defer to Critter#2 and maybe an accountant.
