First question: (I hope I'm answering what you are asking) there are many factors that go into deciding if staffing levels can increase, the budget amount being one of them, but also other expenses.
Second question: are you talking about the vote that Congress just had again today (for the 60th some time) to repeal The Affordable Health Care Act? If so, this is a good article:
Yes, and do you see the Senate vote that required 50+1 passed without requiring 60 votes(3/5 of those 100 entitled to vote)?
And the normal process when you are doing zero base, the agency involved submits their requirements. Each house then gets to vote to fully fund the request or cut the request or can even supplement the request.
Or since congress doesn't desire to get involved(and actually do their job), they just approve last years level of funding plus inflation. Unfortunately, this is what the lazy bastards do and we end up with deficits that outspend the receipts. Obviously if there was deficit last year and the deficits will perpetuate into infinity. Hope this is obvious to you.