Actually it's not just the use of arrays that could save you time and effort. A few simple for...next loops would help a lot too.
For example this section of your code:
set sprite priority 1,1
set sprite priority 2,2
set sprite priority 3,3
set sprite priority 4,5
set sprite priority 5,6
set sprite priority 6,4
set sprite priority 7,8
set sprite priority 8,9
set sprite priority 9,10
set sprite priority 10,11
set sprite priority 11,12
set sprite priority 12,13
set sprite priority 13,14
set sprite priority 14,15
set sprite priority 15,16
set sprite priority 16,17
set sprite priority 17,18
Could be reduced to:
for k = 1 to 18
set sprite priority k, k
next k