Smaller yes, but I wouldn't call it negligible.
> the more the economy grows before the switch to renewables is complete, the harder it becomes to make the switch.
That one I think you got reversed. Think that one through, the economy now is way greater than it was in 1980, do you really think we were better prepared for the switch back then?
I wasn't clear. We become better prepared to switch but the switch itself becomes harder. The 1980 economy was smaller, therefore it would have required fewer renewable energy sources to replicate using only renewable energy. Sure, renewable energy is more available today than in 1980, but that's due in large part to people since 1980 being willing to invest in something other than fossil fuels, despite the lower margins.
But that’s the trick, for instance, now that solar is under the cost of gas, improvements in solar have slowed down, but now everyone is trying to make batteries.
It’s very unlikely that the pattern won’t repeat itself, in 2050 (or 2070), we will probably be in a better position to do the switch, even if total energy consumption has grown.
I don't disagree with your basic premise. Personally I think the answer to 1) is 140 years, so no reason to panic or dawdle. But it's important to remember that the more the economy grows before the switch to renewables is complete, the harder it becomes to make the switch. And, a better invention in renewables without the energy to scale it up won't do us much good, a significant part of our nonrenewables needs to be invested in renewables or the next 140 years of invention won't be much use.