Leave the display out of it to start, and display the answers in the serial monitor for simplicity. Make sure your sums work, then you only have to deal with one type of problem at a time.
For the first part, take your reading which is between 0 and 1023, and divide by 1023 and times by 100; effectively divide by 10.23. That would be the percentage.
For the second one, have a look at the map() command.
AWOL:
Did you mean "the values it should expect is between 0 and 1023 " ?
Yes
JimboZA:
I'm not sure what you mean by assign its units, but yep at display time is where I'd display the units, just stick a "%" or whatever on the end.
Yep I'm sure you could use map to scale it from 0-100 as a %.
exactly how you explained it, if i have the sensor input range changed to the numbers i want i can then add the units to the end of the string on the display.
So like you said % on the end of the 0-100 scaled input.
Ok i need to write this and check out how it reads.