20-25 gear inches is a safe catch-all low gear, but it really depends on fitness level, expected terrain, and how much stuff you like to carry. If you're carrying a laptop, cameras, tablet, and that sort of thing, yeah, maybe. For me, I pack light, and I'd prefer to walk or get off and rest than to run anything lower than 1:1. I find that if you strive for a low gear about 20 gear inches lower than you'd use on an unloaded bike in similar terrain, you'll be alright with touring bags.
FWIW that half step set up with a 4t spread and 28/44/48 chainrings really is only going to work with a wide range 5 speed rear, say 14-17-21-26-32 that was once typical. For 6 or 7, you'd need to go to a 3t spread like 45/48 for half step, or most of the gears will cancel out as in the charts above. ^^^
Personally I would do a normal 10t spread, ie, 28/38/48.