Dear Safo Kofi,
It seems your one question, has more than one queries in them.Please keep them to one at a time,also please do post some research efforts rather simply a question.
Let me answer your question,
Every gear has a speed limit, and vehicle will not speed up like other gears with respect to first gear.
First gear is meant to get start a vehicle from still.
Also accelerating in first gear will lead to:
more fuel consumption
It happens because engine has a specification for each gear to operate,If you exceed them then obviously components will wear out.
Engine has systems to control heat from engine,
Coolants can keep engines in optimal temperatures,
Keep an eye on coolants and also in oil levels.