Hi, and welcome to AFN. Friendly and helpful place this.
Re. your question, I suspect that Black Gold may work fine, but do not know for sure how rich the initial nute charge is. As long as it is not too much for the babies, it should work fine, especially if assisted as necessary with something like MegaCrop later in the grow.
If you are inclined toward soil, but not coco, you could also try ProMix HP myco. It also works a treat, and is definitely safe for the babies. With ProMix, you will need to start nutes about one week into growth. Others on here use ProMix to great success, and I did not too badly with it in my first grow last summer. Technically, ProMix is a soilless medium, but it is more forgiving than coco.
Bottom line is that virtually any medium will work great if it is not too rich initially, and if you properly supply and manage nutes once they have to be added. If I were you, I would try ProMix, and use MegaCrop after initial growth is underway. I would have used it in my indoor grow, but none was available when I set the grow up, so I went with Coco.