Monofin manufacturing advice !

I make my fins differently (I make the DOL-Fin hydrofoil monofins), so others may have better experience with your particular application. But, I am an engineer and I work with composites a lot. So, I know a lot about them.

IMHO, vacuum infusion is a bit of overkill for a monofin. It works best with large project parts. For a monofin, your part will come out just as nice and with a lot less effort if you lay it up wet and then vacuum bag and debulk the matrix (assuming you are making one fin at a time). For the best parts, and still less work than vacuum infusion, use pre-preg composites (especially if doing carbon fiber). The down side is the need for freezers and ovens as well as a vacuum system. And, if you go the cloth and resin approach, mixing things up yourself, you'll probably save a lot of money.

As revan says, vac bag is the way to go. As for laminate and plies, personally i would suggest measure existing thicknesses and work backwards. I would have thought that the hard part would be the foot pocket, or will you use one off the shelf?
I design boats, not fins, so thats the limit of my knowledge

For the hand lay-up I would advise Gurit (former SP-chemicals) resins.
They have a wide range of hardners,from ultra slow to very fast.
The Slow hardners give you windows of a few hours ,so you can take your time.
That way everything is nice and tidy and the way you planned it.
Instead of having to close the bag because your resins is starting to set
Good luck.

The number of plies will depend on the materials you use and the stiffness you want the blade to be when you are done. The manufacturers of the materials will be able to get you the material properties, but the calculations for strength and stiffness of an assembled composite panel can get a little involved. Most people in your position just go by trial and error until they get something that feels right. You should expect to make 3 to 6 monofins before you get one that is satisfying.

You may want to try using a lightweight fabric like a 120 balanced weave so that you can still have multiple layers of thickness at the edge and not have it be too stiff. You can use a heavier weave for the tapering to keep down the number of plies, or just use more layers of the 120. If going all 120, I'm thinking 3 layers at the edge and tapering up to 10 or 12 layers by the foot pockets. This is a WAG, but may be a reasonable first try.

Look for a resin with low viscosity to make it easy to wet out the layers without disturbing your layup. Vinylester resin tends to be low viscosity, has good temperature stability when cured and is less expensive than epoxy. If I were you, that's what I would use.

Also, most people don't know that there are 2 kinds of fiberglass. Almost everyone uses E-glass because it is inexpensive and it works. For most people, stepping up means going to Carbon Fiber. However, unless you are making satellites that cost $10k per pound to launch, you can get similar structural performance from S-glass for a little extra weight. S-glass will get you material properties 3/4 of the way from E-glass to CF for about half the cost of CF.