Joined: Aug 2010
Posts: 12,720
Likes: 2,104
From: Madison, WI
Bikes: 1961 Ideor, 1966 Perfekt 3 Speed AB Hub, 1994 Bridgestone MB-6, 2006 Airnimal Joey, 2009 Thorn Sherpa, 2013 Thorn Nomad MkII, 2015 VO Pass Hunter, 2017 Lynskey Backroad, 2017 Raleigh Gran Prix, 1980s Bianchi Mixte on a trainer. Others are now gone.
It obviously depends on how steep the hills will be. I find an 11/32 range cassette to work quite well on almost every road that I have come across. If you find that the hills with that cassette are a bit too steep, you could change the 28t to a 24t. But you said light touring, not loaded, so I suspect that the existing 28 granny will suffice.
I am not familiar with the exact bike you have, I assume it is a 9 speed cassette. I use an 8 speed 11/32 cassette with an Sram 11/32 cassette. Most of the cogs on the 8 and 9 speed Sram 11/32 cassettes are the same. The difference is that the 8 speed has a 26t cog and the 9 speed has 24t and 28t cogs.
Do not forget that you will need a longer chain.