Basic brake question

Hi all,

I've got a few brake related questions I was hoping someone could provide guidance or opinions on. I'm planning how to best replace or upgrade my brakes on a reasonably small budget. My current ones are a bit squeeky on the front and the back driver side disk has started to rust.

1. Can I replace the pads only / would this be worthwhile? or do I need to do the disks too? I've been looking at the EBC red stuff pads but not sure if they would be a waste on older OEM disks.

2. If I was to do the disks too, should I be doing all 4? or could I get away with doing 2 now and 2 later? Any recommendations on replacement disks? I've been looking again at the EBC D series OE replacement kits, but the USR kits aren't much more money. Additionally, do these kits drop straight into the OEM calipers?

3. Is there much advantage (or disadvantage) going for the drilled/grooved over standard? either in perf or visuals? The car is used as a daily driver so a bit nervous adding grooves might be overkill.

Any info greatly appreciate, I've never done anything brake wise, so looking to learn a bit!