buckets and sand and dirt

if i wanted to start a new island or join another co op, how many buckets sand and dirt can i have, because i have a lot of buckets and dirt for farms

 

As long as you aren't island farming it doesn't matter. I always keep my dirt/sand/buckets/etc when making a new island - I'm not island farming so it's not illegal.

 

i want to join another coop (switch), not make a new island, and im mostly concerned about illegal trading, since i would be trading the items between islands.

 

kinda sucks because i used so much grass and a good amount of buckets on personal builds and farms

 

There is no official rule stopping you from taking your items to a new island as long as you are not abusing it. Sure, you're not supposed to but you stated that you are simply wanting to move your belongings to another island so like I said, you should be able to if you want.

Of course, though, I'm not a moderator, however you can still look at the official rules which clearly defines island farming as the repetitive action of restarting your island for the sole purpose of retrieving illegal-to-trade items.