Nice work on Garibaldi!
I’ve never done a climb with a HR strap (but I am curious as to what it would record when I’m gripped out of my mind – a new max HR perhaps?) so I just estimate a TSS. Which I recognise is just an estimate but figure if I’m consistent then it is better than nothing and over the longer term it doesn’t matter too much.
In answer to your questions though: I would be inclined to subtract from the calculated TSS – and your suggested 40/hr to account for the rests/belays seems reasonable. I can’t think of any other factors to account for.
For comparison, this is how I estimate TSS.
I don’t count the long obvious breaks (eg the half hour on the summit) and then use:
40 per hour for hiking (which I would put glacier travel under) and add for elevation and pack weight if needed.
50 per hour for technical climbing. For this I halve the total time taken to adjust for standing at belays etc. eg 6 hours of pitched out climbing would be 150. I don’t adjust for vert.
30 per hour for scrambley stuff. I figure it’s similar to hiking, but slower, so less of a score.