Grow the pup slowly - don't feed large amounts and buy special food for large breeds. Doesn't matter if it's a pure or cross, if it's got dane AND mastiff if you feed to much too soon you'll get hip problems.
Also, when we got our dog as a pup (dane x alsatian) I carried him around everywhere I could get away with - I took him in my backpack (not knowing there was such a thing as slings for babies that I could have used!) on my front into shops, to uni, to DP's indoor netball games etc. We didn't have a fence and I was home all the time so I could take him out for him to do a poo or wee at regular intervals and when he'd start to get fidgety and we have the BEST homebody dog ever now He never wandered far from the doorstep and he's just brilliant with kids. As in, he'll put up with so much then take himself off to seclusion when he's had enough.
He came from a litter of 10 and at least half were put down for severe hip displaysia. I think those pups went to families that didn't listen to the advice about feeding, as well as genetics - because our Odin was from the very same litter and we were very vigilant about his eating, I had him x-rayed regularly and had him on cartrophen injections when his hip was a bit shallow as an older pup. Management I think is why he's still alive today, and only suffering from arthritis as a nearly 7yo
Oh, and after he was about 15 weeks old he was not allowed on the couch or bed and now he doesn't want to be, so we don't have to deal with big dog on furniture!
He didn't go to puppy school, but I did take him to the local obedience club as soon as his vaxes were done at 16 weeks and it was invaluable - seek a club that uses positive reinforcement, rather than one that uses choke chains. My club was big on only having a leash for PR, and training without having to physically coerce the dog to move in any direction.
Have fun with your pooch - now that we're on a farm I've said to DP that we can have a rescue Dane