That's weird, because I upgraded and found Photos at the bottom of my display in place of iPhotos, but I went to Launchpad and launched iPhoto from there and it worked perfectly. I did ensure all my products were updated, and a full Time Machine backup made before I allowed the upgrade to take place.
I allowed Photos to import the iPhoto Library to create a new Photos Library, but have since deleted that and returned to using iPhoto with its own copy of that library. Naturally, make sure the iPhoto Library is there as well as the Photos Library before deleting anything.
On my iMac and MacBook, Photos and iPhoto are co-resident and work fine - well, Photos works as fine as it can, which isn't to my taste. They don't allow changes made in one version of the library automatically to be reflected in the other though (as happens with iPhoto and Aperture), so to avoid confusion, it needs to be one or the other.
I also have iDVD on my system and that still works, though Apple stamped on it long ago. It doesn't come on new machines and can't be bought now, but existing licences are honoured, at least at present. Apple may think DVDs are old hat, but our 93-year old grandmother likes to have them so she can see the great-grandchildren on their vacations.