The Tributes are great to learn on so I wouldn’t worry about getting another kendama yet, unless you really want to see how the different tama finishes play (painted vs natural vs tacky).
And changing the string is more cosmetic for kendamas. A new string won’t really effect play unless you’re changing to a different type of string, and even then it’s minimal. I just change mine when they look a little dirty or I want to change the color.