Thanks everyone for your responses. They were all very helpful.

I have a PDF of my "Online Ticket" and for both the outbound and return trips, they each have their own "Zertifikat" 11-digit alphanumeric code -> would these be the pickup numbers?

With my 8 euro outbound/return reserved seats, my R&F online ticket, and Lufthansa e-ticket all printed out, I am prepared for my ICE trips, correct?

The last thing I need to do is go to one of the long distance kiosks, enter my 11-digit code, and retrieve my official boarding pass... anything else?

I guess the only thing left is crossing my fingers that a strike doesn't prevent me from getting to FRA from LHR (or vice versa)!