Peter - further meetings with his father is a very important question, of which I've no answer. And Sokichi died in, I believe in 1904. Those last years are very intriguing.
Here's the best info
I've read in English regarding Sokaku's early behavior, his training directly from his father, etc. The article notes Sokichi's education, older brother Sokatsu's martial abilities (where did HE get them), and the repeated social distress that Sokaku "caused" his father.
One passage is particularly worth quoting and one sentence there is highlighted:
Around the beginning of the Meiji Period, a grand scale “kanjin Sumo”  tournament was held during a festival held in Yanazu. Sumo wrestlers gathered from all over Aizu to attend this tournament. The last events for entertainment called “shichinen-gakari” and “junin-gakari” were held; here one wins by beating seven or ten contenders consecutively. A 17- or 18-year old slightly built youngster jumped in to take part in the special tournaments. He had very sharp movements and wore a loincloth but no “mawashi” belt. He used variations of techniques such as swift front movement, “sotomuso” – an aiki application technique, “kirikaeshi,” and some leg techniques. In no time the contenders were on their knees, crawling around the ring, or flat on their buttocks. As a result, he made a clean sweep of all the matches, and holding all the prizes in his arms, he disappeared into the crowd without giving his name.