Don't index just all integer fields. Keep track of the cardinality of a
column. If you expect a field to have 100.000 records, but with only 500
distinct values it has no use to put an index on that column. A full record
search is quicker.
Hmmm... That's new. :)
Well, to give you a good measure: keep the cardinality between 30 to
70-80 percent of your total records in a column. But sometimes your
field is NULL or empty, so it really depends. You can't just put it into
a standard configuration. And it also really depends on how many records
a table contains etc.
Besides that, benchmarking your development environment (you do have one
do you?) can gives you a good idea on how your hardware and setup performs.