@EvilScotsman If its your friend's first grow probably should start him with something simple he can just add water to.
There are as many soil recipes as there are growers. Here's what I can tell you after growing for close to 20 years: A good living soil will produce the healthiest plants possible, allowing the plant to live up to and maximize it's genetic potential. Genetics and environment play a much larger role on yield and quality than what specifically you put in your soil.
I can make good soil with anything. My organic inputs bin is full of everything you can imagine. I got comfrey root, nettle powder, kelp powder, shredded sea vegetable mix (7 sea weeds or something), willow bark (can make super cloning soil with this one), saffron, vanilla powder, blueberry powder, alfalfa sprouts, chia seeds, dandelion root, red clover, mangoes, bananas, golden berries, goji berries, chaga mushroom powder, probiotics, crab meal, baobab fruit powder, casa harina (ground corn), dulse, white mulberries, red beet powder, raisins, moringa leaf powder, psyllium husk, soap nuts, cane sugar, dextrose, aloe gel, diatomaceous earth, clay, pea gravel, coco, peat, cacao nibs, wild rice, oat groats, horsetail, acai berry powder, shilajit, humic fulvic acids, raspberry leaf, lentils, chamomile flowers, rosehips, black beans, bee pollen, etc etc etc etc That's a list specifically of what I have and can use to make my super soils, teas, or whatever I want.
The benefit of using composted manures over making your own super soils is just that: It's already composted. To make a soil like mine takes 3 months. But, to answer the question about smell, I didn't use horse manure but I used mushroom manure and to be honest it smelled a little at first but either I got used to it or it went away, but only when the tent was open. But honestly, if the environment is on point, you shouldn't smell anything at all until you open your tent, at which point who cares what it smells like? During flower I've never been able to smell my dirt over the pungent aroma of kush.
I think the manure should do fine, but if you are concerned about smell, use black earth instead of manure and feed with a light worm casting tea. With the environment dialed in and the right genetics, you can pull monsters with nothing but coco and kelp and happy fungal and bacterial herds. Hope this helps.
