Nothing else i've tried comes even close.
They are slowly adding more content. I think the plan currently is to have all of N5 in the game eventually.
You can find each makuuchi bout on the NHK website. No need to look for random clips.
The official sumo kyokai channel also posts these to their youtube channel after each day
Correct, muna is also a slang word for penis
There is also スミレ. This one is Japanese 12-key only.