How does the number goes to the correct value if it can't satisfy the demand if it's supposed to have that extra amount?

Because the reported 960kW isn't wrong - it works just like a normal accumulator: as long as it is charged its potential output power shows up in the power statistic but this ...

The game still crashes when trying to return to the surface in a capsule in version 0.1.145 with the following error message:

Error while running event space-exploration::on_tick (ID 0)
LuaEntity API call when LuaEntity was invalid
stack traceback:
_ _space-exploration_ _/scripts/capsule.lua:193 ...

The first level is okay. Showing players how to mine and get their first smelters up is pretty important
Personally, I would have to vehemently disagree - the first tutorial is unbelievably dull. Manually mining ores is technically part of the game, and will have to be covered at some point, but ...