Is there any reason either way?
This year's tax will only account for taxable events till Dec 31, 2017. Whatever stocks etc. you buy/sell this calendar year will be reflected in next year's taxes.
You should buy after. If you owe a lot of money to irs then you can use the cash you saved for your stock purchase to pay for it.
You should give it to me to invest for you. I guarantee 25% returns
You should buy before and after.
You can make a contribution to an IRA for the 2017 to lower your taxable income for the year. What you should do however, is get a financial advisor instead of asking for advice here, since it is impossible for anyone on this forum to know if that makes sense for you and your personal situation.
Don’t see any difference. Buy low sell high. The rest of the details probably doesn’t matter.
Wut? What difference does it make? It's a new tax year already.