Regarding jelqing, there are 2 types - wet and dry jelqing.
The best thing to do is search on this board for those terms to find more info. But dry jelqing being the less talked about thing involves no lube and no *relative* motion between your hand and the skin of your cock. So the skin goes along with your moving hand. I and most people who are uncircumcized prefer this as there’s no lubing/washing hassles and uncut guys have more skin to move along the whole length of the shaft. I have a feeling that dry jelqing is more efficient in terms of pushing blood internally, rather than stretching external penis skin.
Your length of 5.5 is NBPEL (non bone pressed erect length). A better indicator would be BPEL (bone pressed erect length) which is measured by pressing a ruler into the pubic bone (ruler held on top of the penis shaft). Fat guys could have a low NBPEL but high BPEL relative to someone with a 6 pack! Good luck (I need a lot of that)!!