Two efficiency questions - clustering and ints

I have a good-size DB (some tables approaching 100M rows), with
essentially static data.

Should I always cluster the tables? That is, even if no column jumps
out as being involved in most queries, should I pick a likely one and
cluster on it? (Of course, this assumes that doing so won't cause
bad correlation with any other oft-used column.)

Another question, about integer types - if no cross-type coercion is
involved, is there any reason not to choose the smallest int type
that will fit my data? In particular, I have a column of small-
integer ratings with, say, values in [1, 10]. If I'm only comparing
within such ratings, and possibly computing floating point averages,
etc., what are the good and bad points of using, say, SMALLINT? What
about NUMERIC(1) or (2)?

Thanks in advance for the usual brilliant replies!

- John D. Burger
MITRE