All of the above I can't see much of a problem with, but I'm concerned
that after some other things are completed in the bathroom it may
actaully become too toasty, so I'm wondering if there's anyway I can
fit a programmable thermostat into the system. I was thinking of
something like this from TLC (http://tinyurl.com/8qgje).

OK in principle. You need to check:

1. The contacts of the prog stat are suitable for the load. I believe the
CentaurStat can do 8A resistive, which is fine for a towel rad, but you need
to check. Don't take my word for it.

2. The stat is suitable for the zone in the bathroom in which it is
installed. Zone 3 makes this a lot easier than Zone 2.

3. The circuit should be 30mA RCD protected.

Christian.

P.S. Look at the full range of stats. Choose one with a simple one push
boost function. You often just want to press the button when you go in and
have warm towels by the time you've finished, with it staying on a bit
longer to dry them afterwards. This is especially the case between spring
and autumn, where room heating per se is less important.