Does the lid seal tight?

The lid is fitted, but specifically designed to not seal. The weight of the lid would be dangerous if too much pressure built up under it so it is made to allow some steam to escape.

Can I put it in dishwasher?

Hand wash recommended. I would never put it in dishwasher to maintain the quality of the pot.

Is 7.25 round Dutch oven heavy??? I have arthritis in my hands so I am debating about this.

Yes, this is pretty heavy cookware. The pot and lid together weigh over 13 pounds, and then of course significantly more when there is food inside.

Is staining more of a problem with white than it would be with a darker color?

I personally don't think so....the sand color is pretty light as well. I have both colors and they get equally stained if I'm not careful. I guess the trick is to clean the pot well so that you avoid any permanent staining. A little bit of BKF powder and they always stay stain-free for me.