I was reading advice for first-time, long distance bicycle tourists. You might want to consider a route less strenuous than the NT or the TA, and that leaves out the PCBR.FWIW, myself and two companions did the TA as a first tour. We all had a lot of outdoor experience, but one was not a cyclist, one had not ridden in a year, and one had been riding a lot. The two who were not in riding shape got in a few 30 mile rides before the tour, but didn't really have time to train since they were finishing up their senior year of college. All were in in the groove 10 days to two weeks into the tour. That said we all were already well familiar with all of the camping and cooking skills which helped.
Motivation is the biggest factor in whether you will be successful and enjoy the trip.