Here's a great book I have and it's about seaweed as used in agriculture but the book first goes into how plants grow and the how and why's. Then it goes into kelp and how to use it with your plants and more importantly why.
Seaweed in agriculture & horticulture (Conservation gardening and farming series : Series C, Reprints): William Anthony Stephenson: 9780960069835: Amazon.com: Books
I'm and organic gardener both indoors and outdoors. I have a journal here and cover my soil mix and how I use it indoors in containers growing cannabis. Welcome to check it out and for sure ask questions ...
Teaming with Microbes... It's a good book.. I like the book I pointed to better. It explains how plants grow and how the soil works ... easy to understand. The author started the company Maxi-Crop.. which is a company the revolutionized seaweed cultivation and processing. Humans have been using seaweed to grow plants and animals for several thousand years with success. This book will also tell you why that is and how it works.
Just throwing another tidbit out there..... there's "organic" farming and there's 'Biodynamic" farming. Suggest you take a look at the biodynamic version via google online there's a lot of info you can read online.
You will (well hopefully) find that composting is the key. Everyone can compost... its the key to organic/biodynamic farming.
"You cannot amend your way to a viable soil. Get the Compost/EWC dialed in and you won't have many questions that need an answer." Clackamas Coots
Yes you can purchase good compost. You can always make your own much better than bagged.