Base sizes really depend on rules used, but generally pike can be on slightly smaller bases than shot (possibly 20mm sq for pike, 25mm sq for shot) although it's not compulsory.
Pike tend to look better in a decent block (anything less than 20 figures looks like a reenactment society rather than a military unit) with 1-2 shot per pike (usually lower number of shot for Royalist units - pikes were cheaper/easier to obtain).