We just got a new puppy of lab/newfie mix…what are the things we need to watch for as for as health issues go?..
Hip dysplasia and bloat and epilepsy come immediately to my mind. Epilepsy is very common in labs (inherited neurological defect), bloat is a problem in virtually all deep-chested breeds, HD is an issue in most large and heavy dog breeds (inherited improper hip socket development).
Bloat risk can be minimized through careful feeding throughout life. You should educated yourself about it so you know the warning signs. It is a life-threatening emergency if it occurs.
Specific large-breed puppy nutrition guidelines can help with proper early bone development and can reduce the impact of hip dysplasia and other bone disorders over the lifetime of the dog. Your vet will have the info.
A quick google search showed me that Newfs have significant inherited heart defects. I know that Labs are a cocktail of inherited health problems but epi is the one I hear about the most. You can’t do anything about epilepsy except medicate, so hope for the best.
If either or both parents was bred by a “responsible” breeder, they may have done some genetic health tests or have other information about the genetic health of that individual. Otherwise, crapshoot.
Congratulations on your new puppy.
Moving to General Questions.
I can tell you what to expect in terms of behaviors at least (having had both a Newfie and a Black Lab in my lifetime)-most notably you can anticipate him running through every single rain puddle after a hard downpour. They’ll also will have an insatiable tendency to gnaw on anything they can-so I’d get some of that anti-chewing chemical (bitter apple IIRC) unless you want teeth marks all over your wooden furniture. And my lab loved to find some dead thing somewhere and roll around in it whenever he got the chance.
Labradors are famous among dog trainers for being more food oriented and food motivated than almost any other breed. Newfs are famous for being good natured and drooling a lot. They both are bred to love water so I hope you have a place for your pup to swim. Newfs are traditionally used for water rescues.
All puppies chew (they are teething). The rolling in dead things is individual.
Labradors need a firm hand in training early on. I don’t know how adding Newfoundland genes will affect this, but you certainly want a large breed pup walking at heel and responding to basic commands before it gets big enough to knock you over or drag you down steps.
Lots of exercise is recommended. A tired dog is a good dog. 
Get him used to having his ears cleaned from a young age, because you’ll have to deal with ear infections at some point. If his coat is more newfie than lab, then regular brushing will be extremely important. Tangled or matted fur often leads to skin problems, especially if he gets wet a lot.
As with any large breed dog, restrict his exercise for the first 12-14 months. Once he is skeletally mature, he will need a lot of exercise.
x2 on the ear infection thing-esp. if he does spend a lot of time in the water.
If you do own a pool or have unconstrained access to one, then Labs and Newfies can be trained to swim underwater (yes, hold their breath, surface dive, the whole thing), something I did with my Lab. [PM for more details]
Be careful on feeding. As above, hips are always a concern, and it’s better to carry around less weight.
You might be tempted to think all is OK because newfies can be so big. Not so, and, labs for some reason get fat very quickly, and will continue to eat forever.
It’s much easier to keep a dog on a diet than it is for yourself. They really don’t hate you, despite your guilt.
Press the side of his chest; if you can feel the ribs with not too much pressure, he’s fine.