EastSideRacer

Now sorry if this is a stupid question, but I am just getting into the engine mods so I am still learning.
Now I wonder when pistons become necessary to upgrade?
If investing in cams, valve springs, retainers, valves.
Does the connecting rod and pistons require upgrade?
Or only if they are damaged?
If replacing pistons how do you chose a bore size?
When choosing valves do you get the +1 if your head is ported?
When looking for compression ratio, how do you know witch one?
What is the difference between lower & higher (lol) compression?

Thanks guys