heatsink

Should I use a 3mm heatsink for my portable to save space or 10mm so it has the same height of my fan and cause the most air flow through the heatsink than over?

Planning on guiding the air out the bottom of the case (when I make it). Is this heatsink too small?

So I have two unrelated questions. 1. I'd like to add 4 3.5mm jacks to a cube. I have 5v amp. Wiring I assume is easy enough, just 4 pots and jacks in parallel but I'm a bit hung up on what jacks and pots to use. I'm pretty confident I can just use standard 3 pin headphone jacks just fine, but...