Back to the OP's questions:

What you are planning to do should not be too difficult at FRA. I think the long distance station is the "Fernbahnhof."

At FRA, DB has at least one, probably several, places where you can buy tickets from a live person, who probably speaks pretty good English. As I recall, these are fairly obvious en route to the long distance station. As I recall, to get to the station, you take escalators up and over the street in front of the airport (where cabs and buses are). You should not need to go outside unless there is a detour for construction.

Depending on what time you are catching a train, a seat reservation may be advised, as the trains out of FRA can be crowded, especially during commuting hours. If you look into the times on DB's site (http://www.bahn.de/international/view/en/index.shtml), you can see whether they recommend a seat reservation. If so, you can buy a seat res for about 5€ without buying a ticket. It is use it or lose it, so if you miss the train or decide to take an earlier one, the 5€ is gone, but at least that is not the entire fare. If you have more than 2 train rides scheduled, you might look into a rail pass.

On the platform, there are maps which show where the cars are supposed to arrive, but these are not always accurate. The platform is covered but open at both ends, so if the weather outside is cold and windy, you will likely feel it. I suspect the other threads on European trains discuss these details at length.

Enjoy your trip.