Gentlemen - hats off, and a cyber nod to you both-.......
Welcome to the forum. Yep, lot's of nice peeps here, enjoy.
I used to live near a beach that had sargassum washing ashore, tons of it and there were folks that used it as a mulch and composted with it. You have to wash it well and then go from there.
Regarding organics, I'm not a purist. The green movement, the zealous organics push, is all about the money and control, don't want any part of it. One must reach a balance in their life and that includes gardening. I will not use any kind of pesticides on my veggies unless necessary cause I learned years ago that less is more, plus it takes time and money to apply. Do I think the general use of pesticides is a personal health risk, depends on amounts, frequency, application rates, etc. Read the label.
Having said that, here's my soil recipe drafted as a guide many years ago. Make sure you understand plant requirements before you go off and use this and that. IOW, seaweed's main function provides trace elements. When it comes to enzymes, vitamins, and other crap some vendors claim plants need and their products supply, it's just that, crap. Plants need 16 essential elements, the rest if manufactures.
My plants show no deficiencies when I don't use seaweed, quite the opposite, they are so vigorous that I have to flower 3 weeks from the time the seed pops the surface, and I still get 4' tall plants.
I use alot of brown sphagnum peat moss, a large bag of Schultz potting mix, and a bag of cheap potting soil (screened to get rid of the chunky stuff) to make up enough for 30 to 40 gallons of a final mix, which I mix on a cement floor using a shovel and store in large garbage cans. To this base which provides humates, an acidic hit, trace elements, etc. and a little silt to tighten up the mix and retain moisture, I add:
6 or so cups blood meal, 3 or so cups bonemeal, 4 cups dolomite lime, 1 large bag each of vermiculite and perlite (available at Casa dePOT) and alfalfa meal which contains a hormone called triacontanol (purported to increase vegetable production up to 60%). I buy alfalfa feed pellets from a farm and ranch supply store, put about 4 cups of the pellets in a bucket with a gallon of water and give it a good squirt of Ivory dish soap to cut the surface tension, let it stand for 30 minutes, and then dump the slurry into the mix on the floor. I sometimes add composted horse manure, maybe about 3 or 4 gallons of it. The final, slightly moist soil mix is turned well with a shovel and stored for a couple of weeks in garbage cans to "mellow".
Good luck,
Uncle Ben