Unlike shrimp, it matters not whether your crawfish were wild caught or farm raised, as the culture of both is essentially the same. Crawfish prosper with a specific pattern of flood and drought to their environs, the same pattern of flood and drought that produce the best harvests of rice. Louisiana rice farmers control the flood and drought of their fields with levees and gates, and crawfish farmers use the same technique to provide habitat for their crops. In fact, many rice farms grow crawfish in between crops!
In addition to crawfish, you'll need a "boil" to season your pot. When I was a kid, Momma G always used bagged boil, which is pretty much a gigantic tea-bag filled with dried spices. In later years, Zatarain's invented liquid boil, which is very concentrated. Either one of these choices would be appropriate for your low salt boil. There is also now a powdered or granulated boil, but it is salt based and should be avoided if you are trying to reduce your salt intake. You will probably want to add some salt to your boil, but those powdered boils are VERY salty!
You'll also need a "rig" to boil your crawfish in sufficient quantities. When I was a kid, if you needed a rig, your daddy found a friend who worked at a welding shop, or the gas company, or somesuch, and they devised and made a "rig" for you. Then you went to the restaurant supply store and bought a big pot. Nowadays, turkey fryers and crawfish cookers are readily available in many cities and online. Lesson learned this weekend: while you may be able to use the burner from a turkey fryer for crawfish, you really don't want to use the turkey pot like I did. It's too small to hold a sack of crawfish, and it's too tall to boil efficiently. Ideally, you want an 80 quart pot that is the same diameter as your burner.
Start your pot early because it takes a long time to get 40 quarts of water to boil! Fill your pot a little over halfway full, and add 4 boil bags, plus an 8oz bottle of liquid boil. Quarter 5 onion and 5 lemons and add those to pot. For a normal boil, you would add a box of salt. You may add less than that if you are trying to reduce sodium.
Crawfish need to be purged in salt water before you cook them. Use a clean plastic trash can, empty an entire box of salt in the bottom, and fill about 3/4 with water. Careful release the crawfish into the salt water.. They will immediately begin to spit all the mud out of their systems, and the water will foul with mud. Once the water has darkened, empty it out, rinse the crawfish, and fill again with fresh water. If the crawfish continue to purge and foul the water, empty, rinse, and fill again.
You'll also want corn and potatoes to finish out your meal. Use the smallest red new potatoes you can find, or cut larger ones in half or even quarters. You can use fresh corn or frozen, and traditionally the cobs are cut in half.
Once your water is at a rolling boil and your bugs are purged, place the potatoes in the basket of your cooker and boil them for about 10 minutes (they take longer to cook than the crawfish!) After that time, carefully remove the basket from the boiling water, drain the crawfish, and add them to the basket. (Watch for escapees!) Return the basket to the boiling water, add the corn, and watch for it to come back to a boil. Once they are boiling, time for 7-8 minutes.
When the time is up, turn off the heat and let the crawfish sit in the boil for 15-30 minutes, depending on how spicy you want them. The longer they sit, the spicier they get! Start testing them at about 10 minutes, and once they are spicy to your liking, dump them out onto a newspaper covered table and start eating!! If someone wants them saltier and spicier than you cooked them, they can sprinkle their pile with Tony Chachare's seasoning!