Wow, just got mine. It's really not that hard, after all, it just takes so many tries because bad luck can hit you hard easily. (And that's why it's annoying, most of the time failing isn't even your fault ... for instance when a cowman runs into you from behind.)
If it is of help to anyone, I thought it was the best to leave the racing track alone and only collect stuff from the inner part od the island and then the sea and what you can get at the coast. In the end, make a short trip to where the car wash and the boxing arena are, then you should be large enough.
Now for the rest of the collection. Noone knows where Komusubi is located? : (
Haha, this might make you kind of mad but im almost 100% sure that Komusubi is the guy at the end of the sumo level, you have to be big enough to roll him up instead of just knocking him off. Check the end of this video right around 5:40
No, he's not that one. ; ) Just found him. He's in Make A Star 9, I wrote it in the other thread. (Thing is, I knew there were Sumo dudes there and it was the first place I checked right after checking the Sumo level. But I didn't find him then.
This one did suck but i used the youtube videos, and made my katamari just over 8 m and then dash attacked and captured the cowbear in the small river part. It took me like 3 hours to get up to 8 m without hitting a cow/bear thing. Be carfull once you hit 8 m not to dash the cowbear to close to the bridge or else you will roll up that stupid cow umbrella. hopw this helps.