Ok, I see one MAJOR issue with that list, so I will deal with that first.
3-5 times a WEEK???? Have you done any breed research at all? Even the smallest, laziest dogs should be exercised at least once a day - and the breeds that you are mentioning are bigger, medium-high energy dogs...getting them as a puppy will mean that you are exercising them 3-5 times a DAY. Unless you mean that you will be able to do 2-3 shorter walks a day, and then do a BIG romp to the beach/dog park/hiking etc 3-5 times a week on top of that, in which case, that's ok.
As for the rest:
1. These three breeds should be fine with water, although the first few times with any breed you will probably be best off going in there with them until they get the idea! Labs and Retrievers can often be seen down at my beach playing fetch with a ball thrown into the ocean. However, some dogs just don't like it. Its not a breed thing, it is a personality thing - and that isn't something you can guarantee.
2. It depends on the pomeranian!! How does he/she get along with big dogs is really the question. None of these breeds are really known for a prey drive, but no dog will get along with a bratty or aggressive dog. Is the pom well socialized? How old is he/she? There are rarely issues with bringing a new puppy into a home where there is a balanced adult dog, but the resident dog can have problems, especially if they are not the mellow type to begin with. And how old is the Pom? You don't want to be bringing a puppy into a home where there is another dog that is not fully trained.
4. Ooooh lordy that is a HUGE question. Here are the things that I think are very, very important.
- Puppies are HARD WORK. Especially large and high energy breeds. Expect to have your life revolve around the pup for the next few months.
- You will get very little sleep for a while. Puppies need housebreaking, and can't be expected to hold their bladder all through the night for the first little while. So you'll be getting up throughout the night to go pee.
- Dogs are a big commitment - living at home, you have a bit of an advantage if others are willing to help with puppy-sitting, but it makes it incredibly difficult to just go out at night (who will take care of the pup? Has it been walked? Can it go in its crate for that long yet? When will I be back? Is that too long a separation?), or go on a spontaneous vacation, or travelling....and this is for a long time - if you get a puppy now, you will have it until you are 30-40 years old. Really think about that.
- If you do mean that you can only exercise a dog 3-5 times a week - YOU CANNOT GET A DOG. Simple as that. Here is a little breakdown of our original schedule with our puppy when she was 8 weeks:
5am - get up to pee. 8am - get up to pee. Feed pup. 10am - pee and a half hour walk. Playtime for 20 mins after. Noon - pee and lunch. Training time for 15 minutes. 2:30pm - pee. 5pm - pee. 7pm - dinner and an evening walk - 30mins. 10pm - pee. midnight - before bed pee. Sometimes there was a 3 am pee in there too!!
Now that she is housetrained, the schedule gets a little easier. But she is just over 3 months, and gets 4 walks/pees a day. Only one of those is a pee-only situation (right before bed). The other three are walks of 45mins - 2 hours, depending on our schedules and how she is feeling. We do most of our training on walks, but there is also a lot of housetraining, and extra training. She is basically a full-time job. If you don't have the time to commit like this, don't get a puppy or a big, energetic dog. Get a grown, trained, low-energy rescue dog. Puppies are insane, especially if you are a first-time owner - they are a LOT to handle.