Instead of spending time gluing qtips on for sprues, you can just punch them after you have both halves of your mold done. I use 12 gauge hollow dispensing needles and it's *way* faster than messing with qtips and it also doesn't ruin a cap in the process.
Also, for "keying" your mold, it's helpful to make sure that you can only start to put the mold together 1 way. Having 4 columns that are the same size might lead to issues down the road since you can get the mold most of the way together before the mold physically stops you.
Good luck on your journey!