I think the description for the Max Ice Tool Hangs in this plan was copied from one of the rock workouts for a fingerboard, hence the “Many climbers will likely need to subtract weight” wording. I would think most ice climbers doing the 16 week Eiger plan will need to start in the neighborhood of +50 lb.
The +/- 5 lb increments are also a bit fine while you’re dialing in the weight. I did start at +0 lb and I spent 5-6 workouts trying to find the right weight. I switched to +10 lb increment after 2 workouts because it was clear the starting point and the +5 lb increment were too low. I weigh typically 155-160 lb and found the “Additional Ice Climbing workout” which precede the “Max Ice Tool Hangs” to be far more difficult to complete.
I would also agree with gripping the shaft rather than the handle to increase difficulty.