Yes, call a certified technician to do the replacement of the freon.
900
600 square feet.
4000btu
5280 maximum
The general rule is 600 sq.ft. per ton of refrigeration, so an 18000 BTU A/C will cool approx. 900 sq.ft. . There are many variables, such as insulation R value, normal summer climate in your area, age of the structure, etc., so this is just a guide. To know for sure, have a heat load calculation done.
1500 sq ft.
Yes, a 4.5 ton air conditioner would be the minimum size for 2000 square feet.
around 400 SF, not ft
3 ton
NO
yes