Soft rubbers have their place but my preference would be ungers hard rubbers, they should do better with the heat.
As far as how long they should last before you buy more…
I would at least buy one pack before it starts going bad, you don’t want to get stuck cleaning with one that’s streaking while you wait for the new ones to be shipped.
Working with larger commercial windows, there are other recommendations out there as to the type of squeegee and rubbers, but it sounds like you’re at a good starting point.