Paying off your student loans doesn’t really affect your taxes much. The only thing you can deduct is the interest paid, so really it just means you’ll have one less deduction in future years. But the interest paid is almost always larger than the deduction, so that’s no reason to hold onto the debt. As for exemptions, I recommend taking as few as you can afford. The more exemptions you take, the smaller your refund (and the higher the chance you actually have to pay taxes at the end of the year instead of getting money back).
But that’s the safe approach. You could also try to figure out exactly how many exemptions you can take without owing anything to the IRS at the end of the year. Or you could take as many exemptions as possible and just plan to owe money on tax day. That way, your money is gaining interest in your bank account (or stock portfolio) instead of the government’s. It all depends on how well you understand finance/economics, how good of a planner you are, and how much time you can devote to it. Personally, I have better things to do with my time.