Consider completing the sealing of the crawlspace by covering the walls as well. The more sealing, the less often the dehumidifier will have to run.

Im looking to do the same thing. But keep the vents open for now. Did you get many responses on this ?

I blocked off mine from the inside with XPS foam board and single-part spray foam around the edges. Very few climates have a legitimate benefit from having them open, especially if you're home is reasonably leak-free or you're trying to improve it.

You need a continuous (i.e. taped, foamed, heavy poly, or a combination) all the way up to the wood sill plates on the crawlspace walls, on all piers and other penetrations. If the sump is in the crawlspace, seal the inputs/outputs of that too. If you can, insulate/air-seal the rim joists around the perimeter as well. Those are a very common place of leakage and heat loss/gain. You can do those just like the vents. Even in humid climates (like the southeast US where I am) the majority of the water infiltration is actually though the soil and walls. Concrete stays quite damp and will wick water even decades after it's poured. If it's not continuous, poly on the floor just makes a clean place for water to condense and possibly keeps sand off your pants when you're down there. Oh, it's also good to make sure the space UNDER your seal will drain well and is soft and clean (like play sand or similar). Water likely WILL get in there, and even if it doesn't get through, it can make a mess under there if it's not allowed to drain. somewhere. If you have to get under there, sand is a lot nicer to work with than mud. Get a decent humidistat and take some readings in various weather and times of day and also if you're A/C is running or not. It may be getting dehumidification from the home HVAC already. Once it's closed up and you know you still NEED a dehumidifier, it'll give you an idea how MUCH of one you should buy.