I would suggest Tony has covered almost every base in his line of questioning. I have one more thing you will need to check out, assuming you receive the sculpture.
A children's museum has, well, children. Given their propensity to climb, swing, jump, etc., placing a large object with moving parts (wind sculpture) on your campus, you may wish to check with your insurer for placement and security of the sculpted object from potential self-harm enthusiasts, or absent minded adult supervision
related accidents. Your insurer, when provided with a photograph and desired location on your campus can advise you on best practices or liability reducing efforts to avoid problems or increased insurance risks.
Now, because I offered that advice a bit tongue-in-cheek (I work with 100 children every week at church), I will also present a thought on the refurbishment issue. You mention it needs to be painted. That one will be easier, providing Tony's suggestion on acceptability are on track. Check your donor base for any painting contractors, or approach a larger paint contractor in your area for donation of services. Arrange a photo shoot of their work to go in the human interest section of your local paper...you get the idea.