1-3 years after it sprouts incredibly
No.
Yes it is.
Yes it is.
plant a grapefruit seed. Water it. Let it grow into a tree in a warm climate
Grapefruit extract does not kill good bacteria, it kills fungus and fungal infections. Grapefruit seed extract kills systemic yeast as well.
A grapefruit is a FRUIT. Think about it grapefruit, fruit, get the hint? Look it up online and you should get the grapefruit tree, and it say that it is know for it sour fruit.
If the wood is old enough, it can be used. Do not use freshly cut wood as it will smoke too much. there are no poisons in grapefruit tree wood, so that is not an issue.
4-6 m
I was going to reply no, but with further research, I will go out on a limb and say, maybe. I suggest buying a dwarf grapefruit tree and keeping it in a container, so it can be brought inside during the winter. It might also survive in an atrium. Interestingly, a citrus needs a chill period in the winter to produce good fruit. However, the bitter winters in your area will kill an unprotected citrus tree.
a grape tree last for as long the roots don't pop out
They grow on trees, just like oranges and lemons.