O.K. here's one man answer:
Bondo is a trade name for fiberglass resin it is used in the automotive industry as well as the boating industry it is the goto material when I make 2 piece molds as it turns rock hard when cured but can be machined easily. De-molding is also easy provided you are using a plastic wormbait as your positive. Don't forget you will need registration pins on a 2 piece mold.
RTV is nice to work with but I only use it for 1 sided baits i.e. chunks, craws it releases well and is flexible but is pricey.
As to a pour hole if you look at a real aluminum 2 piece mold it is approx 1/2 " in diameter and around as deep, again be careful what you use if using resin or it will never de-mold (Use release agent)
As to a vent what I do is straiten out a paper clip (larger type) and use it as a skewer to put the bait together, if you leave it protrude from the bottom of the bait it will act as your vent, it also works well when using different parts of baits to make a new creation.
Also consisder POP (plaster of paris) this is a very cheap but yet productive way to make 1 & 2 piece molds you can find more on that if you search POP.
Just a suggestion being your costs are high, only mix batches of 4 oz at a time when first learning as you will foul up now and again, most of the guys here use 4 ozs as a base for their color recipes which again you will find on the forum.
Good luck!
Chris