Simple Q&A Pathfinder (By RAW) I

[Lord Bingo]

A55 IMO the wording in the buckler entry is pretty clear. You will not receive a penalty to your attack rolls while using a bow or a crossbow when wearing a buckler. However, the general rule that you will not gain the benefits of the buckler while attacking with you off-hand or a two-handed weapon still applies.

So, no penalties and no benefits

A56 There is nothing that specifies how much higher, in feet and inches, you need to be to to gain a height advantage over an enemy, so basically it is the DM's call to decide whether your relative position to your target should net you an advantage.