Max your IRA, then open an account with Vanguard. Taxes are reasonably straightforward. Vanguard will send you a tax statement that contains the information you need. Do not be surprised if you get a "revised" tax statement later. If you have already filed, you may need to file an amended return. As a result, we typically don't file until the deadline.
I believe that it is wise to save additional retirement funds outside or government regulated IRA/401K/TSP/pension plans. It would be far easier for a democrat communist majority government to "nationalize" your government regulated tax advantaged retirement savings than it would be to confiscate other investments. Most people do not have enough saved, and all the commies need is a serious market drop to justify a government take over of retirement funds "for your own good."
That said, I maximize the employer match on my 401k, and my wife maximizes the match in her TSP plan. I wouldn't worry too much about the government nationalizing IRA/401k/TSP plans until your net worth exceeds a few million. Even then, maximize employer match before you worry about retirement savings outside regulated plans.