First formal wedding - is my top choice okay?

Hello! I've been invited to my friend's wedding - end of February in southern Ohio. The invitation and website don't really specify other than formal, but the venue is a fancy hotel in the area. The teal is my top choice, but I'm wondering if the neckline and back cutout make it less formal? Ideally I'd also like to get something that could be worn year-round to other formal weddings in the future, so I'm trying to stay away from fabrics that read too seasonal (like velvet), and am not sure if satin is a bad choice. I added some other options as well, in case one of those is better.

Please let me know if more info is needed!