There is a website which shows you in sample pictures how your view looks like depending on the seat you chose during this event.
Some general points:
The tournament lasts the whole day, from early morning. It's great to see how the younger fighters and their fighting style differs from the older, professionals.
The matches themselves are over in mere seconds. there is not too much that happens between the matches. Specially not if you are there the whole day, and see the activities between the games dozens of times
To sit on the floor for the whole day can be quite tiring for the legs. You will be more comfortable to sit on chairs on the borders instead of sitting on the floor closer to the center. If you plan to go there for the whole day and get some binoculars, you might be good even on the cheapest seats.
Now my personal experience while watching sumo:
Watching sumo is something very special and you will not really understand the sport or grasp the mechanics of it from far away. Why?
Some of the movements are very fast and you will struggle to see what happened if you are too far away.
When the fighters are stuck together, it's important to see their faces better to understand how they are holding up, who is about to give in, or who tries to get a better grip of the opponent. details you cannot see from far away.
There is also a huge psychological warfare going on during and specially the seconds before the fight. To be up close and see how some fighter feign weaknesses or overplay their strength is very interesting.
It's finally a contact sport. Up-close and personal. And if you are not sitting on a TV, you will not have replays. You will have to see it when it happens, as it happens. And if you are too far away, you will not really see what's going on, and there is a huge risk that it will be boring.