There are a lot of ways to grow organically. Various people are going to recommend you do different things, just keep that in mind and try not to let that confuse you.
Liquid organics are very convenient, they don't have to be expensive and certainly good to have handy should you experience any deficiencies. Have used Earth Juice quite extensively, more recently with General Organics. You don't have to make your own soil, or keep a worm farm, honestly (unless you want to). I have used Roots Organic potting mix in the past, a couple years ago, don't remember having any issues with it. Happy Frog also works for seedlings and clones. I prefer to have coco coir in my mixes, which is already present in some such as RO and Sunshine Advanced Mix #4. Otherwise you can buy it in compressed bricks, or ready to use.
Happy Frog, Light Warrior, Sunshine AM#4, Pro-Mix, et al., are all fine for seedlings and clones. Some soils such as Fox Farm Ocean Forest have stronger ingredients and may not be suitable for starting seeds (depends who you ask). It would benefit you to be able to read and understand product labels, so you can know what a product is made of and how\when it is supposed to be used. If you're buying pre-mixed, check out the ingredients so you can determine if you even want the product and if you may need to add anything.
SAM#4, for example, is just: Canadian sphagnum peat moss, coco coir, perlite and dolomite lime (and it has been inoculated with beneficial fungi). This tells us it is strictly a soil-less mix and it isn't designed to supply much in the way of primary plant nutrients. This is the kind of media you could simply amend with some compost, humus or earthworm castings to start seeds in, or prepare with dry granular organic nutrients (Espoma -Tone products, guanos) in various ways, depending on stage of growth, or blend with a stronger soil like Ocean Forest.
You can tell OF is a much richer soil by looking at the ingredients: Composted forest humus*, sphagnum peat moss, Pacific Northwest sea-going fish, crab meal, shrimp meal, earthworm castings*, vermicultural compost*, sandy loam, perlite, fossilized bat guano, granite dust*, Norwegian kelp meal and oyster shell* (for pH adjustment).
The ingredients in bold is where most of the primary nutrients come from, it has already been heavily amended as we can see.
*Forest humus, compost and earthworm castings are all essentially forms of thoroughly decayed organic matter (humus); the result of decomposition by detritivores and soil micro-organisms, various types of which remain in the finished product (e.g. earthworm castings are dominated by bacteria). Humus is carbon rich and contains humates\humic substances which are quite complex substances that play a role in the assimilation and transport of nutrient ions by plants. Depending on the source it will also contain some available and potentially available primary nutrients as well as minerals and trace elements, as well as various species of bacteria, archea, fungi, protozoans, nematodes and perhaps even some micro-athropods. Granite dust provides slow-release potassium (K) and trace elements. Oyster shell is just calcium carbonate, so it provides calcium and adjusts the pH of the medium.
I would recommend adding dolomite limetone (at least 1 tbsp\gal) to any mix you don't plan to transplant within a couple weeks add more the longer you plan to go without a transplant (dolomite provides some Mg as well as Ca).