I have a medium size (2-3 gallon, I'm not sure) container. I want to
plant miniature rose in it. I went to HD today. I found a 6 inch
miniature rose and asked the lady there. She says I have to re-pot the
rose in about a year. Is this true? I don't want to re-pot the rose
again in just a year.

If I want to leave a miniature rose in a container for atleast 5
years, typically how big the container should be?

Thanks.