Ok, I looked at the OP again and saw that I made an ... out of myself asking for travel dates when they were actually in the post. (Doh!)
Unfortunately, there will be no sumo tournament in early April. The wrestlers are just finishing up the March tournament tomorrow (Sunday) in Osaka. The next one won't be until May. They will all be back in Tokyo during your visit but will be getting healed up and back into the training routine. You MIGHT get lucky and see a few of the younger guys walking or biking around Ryogoku near the arena, running errands. They are hard to miss in kimono and with the large size. I would still recommend a visit to the Edo-Tokyo in any case.