1: Depends on what relays you get. I recommend
these 60A ones. They will handle anything you throw at them other than your starter. Jerry recommended them for a horn and they would work equally well for headlights.
2: You mention both series and parallel wiring. The headlights should always be in parallel or they will only get half the power.
3: Whatever method floats your boat. You only need 2 relays (one for both high beams and one for both low beams), so if you want to mount a pair of them somewhere you can. Or you can get a fuse block with both in it and mount it somewhere else. There is no functional difference.
4: The greatest majority of automotive relays are SPDT 5-pin because that lets the manufacturer (and parts house) stock a single relay that can be used in any of the potential configurations. It is purely for their convenience.
Clear as mud?
As a side note, your 65W bulb will draw ~5.5A. You are not talking about a huge amount of juice here.
