About EQ gains, I started with very good EQ, so I don't think my gains came from the improvement of a previously sub-par EQ. However, I've found that as I gained I needed to make my EQ even better by further strengthening my pevic floor muscles. It felt as if in order to fully realize each gain (i.e. translate the BPFSL gain to BPEL) I needed to be able to achieve 110% erections, which would then naturally become the new 100% until the next BPFSL gain.
I believe that's where the limit to gains lies, it isn't strictly a matter of blood volume but of PF strength, there's a point where your muscles won't be able to "support" the added volume anymore (notably the BC muscle that supports the corpus spongiosum and glans), you won't be able to get to that 110%, and you'll be left with what feels like 90% EQ and maybe visually a slightly bigger penis but no measurable BPEL gains. At this point it's useless to try and make more BPFSL gains, you'd just end up with even worse EQ and possibly PF dysfunction.
Yes the scrotum and the fascia surrounding the suspensory ligament (fat pad) are going to stick out more. Their attachment point on the shaft doesn't change but that point does get pulled out, although the bulk of the gains still happens on the actual dick by expansion of the tunica, so there are NBP gains but they won't match the BP gains.