I've never been to Osaka and you've already covered Akihabara on your itinerary. I'd also recommend Ikebukuro.
And knowing that you're trying to learn Japanese I'd also very strongly recommend that you try and speak zero English in Japan and try to exclusively speak in Japanese. Avoid the English language like the plague. It won't be hard as the majority of Japanese people don't speak English (some of them like to think they can ;p). You learn more from daily conversations than you would from months of hitting books.![]()