There are lots of ways but the easy one is the "spiral" or "snail" method.
1- Is there a pattern in good and bad starting points?
You can start anywhere.
2- what if some of the arrays have coins missing?
It depends on which ones are missing. Suppose we
take out, say, the last 7 circles the fly hoped on.
The fly can hop onto all those. But if we take out a whole row,
like this:
There is no way possible to get across that missing row.
3- what if diagonal moves are permitted? Other moves?
We don't need diagonal moves or any other kind of moves. It's easy
enough as it is.
Edwin