I too started making molds and baits recently, I can tell you when you start you wont be able to turn back....it's very addicting. The best advise I
can offer is to read, read and read some more. This forum is full of great info.
Are you prototyping your own mold or are you duplicating store bought baits? Are you wanting one or two piece molds?
If your duplicating store bought baits, you may wanna look into some of the aluminum molds for sale. You can find some great buys on used molds on TU in the classified section. The aluminum molds are multi cavity, full of detail, well vented and seal very tight reducing flare on the sides. Minimum clean up.
If you have crafted your own bait you can start with POP (plaster of Paris). If your original is wood be sure and seal it our you risk busting it when trying to remove it from the POP...In my experience i've found the POP molds very useful for rapid prototyping on the cheap. However, be patient and don't rush the POP! If your bait has allot of detail you will sacrifice it if you de-mold your cast early!! I typically I let the POP stand for an hour under a high output lamp for curing. I use wood glue and water (50/50 mix) to seal the mold. This does two things for me...#1 prevents the need for a release agent #2 leaves the mold slick and smooth, makes a shiny bait. I like to use plexiglass for my forms and seal the perimeter with hot glue. I stop at ace hardware and ask if they have any scrap plexiglass I can buy... the outcome is always good. If you have a little money to burn, you can use the Alumilte putty. The putty will give you a working mold in 10 minutes with pretty good detail. But it cost 30 bucks for a pound vs 4 bucks for a bag of POP you can get it at most hardware store or even Walmart. Hobby Lobby has great deals on RTV rubber and casting resins from time to time, watch there site for coupons.
Some folk may disagree with me on this, but it works for me. I started with an injector from Jans Netcraft. There cheap and if you find you're in the market for a new hobby your loss will be minimal. For POP and any other hand made molds that I make it works great. Due to the fact that you are new, your molds probably wont be vented properly and wont pour well. So this injector will help overcome this. And its cheap! I own two of them. You certainly wouldn't want to buy an aluminum mold an anticipate using this injector.
After I decide i'm going to take it to the next level I go with a single RTV mold and I create multiple replica's out of my master with Alumilite casting resin or Smooth-Cast 320. Both work great. I use plexiglass to form the mold area with a molding clay (non drying) base I then push the dubs into molding clay half way and level, I use air soft BB's as indexing points in the clay as-well. Because I use injectors I use a 3/8" dowel for the mane channel that flows to all the baits. Push it into the clay half way as well. Now I pour my RTV or Smooth on 121-30 over the parts
Before I remove the forms I pour just enough casting resin on the top of the new RTV cast to cover the outside of the mold, this gives the mold a little backbone. After the mold has dried and you pull it from the form you will notice the baits are stuck in the mold....leave the baits & dowel and remove your index markers. Flip the mold over and re-form the mold spray it with mold release and re-pour. If you've made it this far your hooked.
Now your ready to make some baits
Be safe, halve fun and take your time. Don't get discouraged if there not exactly like you wanted, it takes time and the fish don't typically care!
I kinda rushed through this hope it helps!
Chuck