I recommend a site called Animoto. I used to do my slideshows myself and as soon as I found this site I started using them. Slideshows at weddings have fallen out favor, but I still offer them at a price that nobody would take me up on. LOL
But Animoto is great because you can pretty much do whatever you want, have as many pictures as you want. They have themes, and transitions and it's very easy. You just upload photos and tell it how long you want each one.
The music can be tricky because they now have software that detects if you are using anything copyrighted. But I know you can upload songs you want and if the site won't allow it they will tell you and you can try something else.
Animate does let you care online as well. But you can pay small additional fee and download the video in HD and re-upload it to any site you want.
Good luck with it.