1. Superchlorinate to get rid of bacteria
2. Use a decalcifier or Swirl Away
There are several commercial products available that you can run in a hot tub to get rid of the buildup in the pipes.
Yes, unless you "winterize" it by blowing the pipes free of water before the cold sets in. You should research exactly how to do this on a hot tub website like the one below
Probably because the hot water pipes are right behind the front wall of the tub.
You make it too hot and melting the fat.
NO, it will not freeze.
Install anti-hammer arrestor in hot water line at tub. It should help.
Hot tub covers can have long lives if they are cared for properly. Hot tub covers are mostly affected by dirt and sunlight so keep it clean and perhaps put a tarp over it if the hot tub is in direct sunlight.
try CLR. it can be bought at any grocery or home improvement store empty the tub and follow the directions on the bottle.
If the pipes weren't cracked from the water freezing and expanding then you could be ok.
What is the age of the home? Some older homes used small pipes and after years the pipes can become partially blocked with mineral buildup. The vanity faucet distributes much less water than the tub. Note the outlet size of the vanity fauced versus the outlet size of the tub. If the flow rate is not available to the tub because of small pipes or other flow restriction the problem will show up as small flow rates at the larger faucets. Good luck, since increasing the flow rate can be expensive WHICHEVER problem it is. If your plumbing to the tub is small, it will be expensive to replace. If the plumbing is blocked by mineral deposits, it will still be expensive.
It's probably the original bath and the steel pipes are corroded and leaving mineral deposits in that bath. Other pipes may have been replaced.
All of the above. Mineral deposits form on all piping and water appliances.