Very much this. I seem to find that P necks seem flatter in profile on the back (no doubt due to the wider nut dimensions) and fit my medium to large hand better than a J. Realistically I'm happiest with a 40/41mm width (best of both worlds), thus my custom builds feature this. Conversely, the J has a slightly bigger, offset body compared to the P. The only way to find which you prefer ergonomically is to try both side by side, but then we're back to the current restrictions making this nigh on impossible. The pickup thing is a conundrum, but you can always fit more (in the case of the P) or different pickups at a later date, should you wish to.
However, as this is your first bass, you'll have nothing to compare it to and will adapt your style accordingly (it's unlikely that the differing ergonomics will make either model unplayable). At this early stage, it's important not to ignore how much you like the look of it, as that will often determine your desire to pick it up and play and the '70s CV with those block inlays is a looker.
Sires get a lot of love around these parts (I've never played one, so I don't have an opinion as to their sound or playability) but, rightly or wrongly, something from the Fender stable will always have a higher resale value and be more desirable should you decide to move it on down the line.