Do you know what ship he is deploying with? There are groups for some (not all) of them and maybe his will be an active group. Just remember - don't post the deployment date - OPSEC.
I'm sending you a PM - check your inbox on your page.
I guess the first advice I would have is to ask your son about the ombudsman for the ship. That person will be the source of info, if there is any, while they are deployed. Do be prepared to not hear from him, he may or may not be able to communicate. I found the best way to communicate is on FB messenger. That little green light is like a ray of sunshine when you haven't heard from them in a while.
I don't know what advice you may be looking for exactly.
Long post incoming. Sorry about that.
The ombudsman (it is the wife of one of the commanding officers on the ship) really doesn't answer a lot of questions from parents in my experience. They really can't other than something general. Even they might not have the answer, or be able to say.
My son was on one of the ships years ago that was "stuck" in the Philippines, when the Marine killed a local girl. I am going to use the term "we" because there were several of us moms that were in contact with each other. We all received an email from the ombudsman that stated, "Your Sailor are safe, and confined to the ship. They will be in the Philippines indefinitely. They all would appreciate receiving (a list of things). Everyone should receive some kind of communication from your Sailor within the week, but that will be the only communication allowed." We still had no idea what was going on, or what had happened at that point. It didn't take long to figure it out though, the internet being what it is.
When my son called me (FaceBook messenger) he still couldn't say much, but of course I told him we all knew the basics. What he could tell me is they were fine, confined to ship, and undetermined when they would leave. He then asked for items he needed. Which of course I boxed up immediately and sent off the same day.
The only other thing we heard from the Ombudsman was they were able to leave port, and we would again be able to communicate.
I guess my story comes with, the ombudsman is really there for the spouse and the Sailors children, assisting them with the deployments, problems with medical care, where to go for assistance etc. Parents just get the basics when needed. Just my opinion. Your son will know where they are going, and may be able to tell you, he may also be able to tell you "expected" return date, but there is usually no communication from the ombudsman with the parents. Of course you know if you son does tell you anything, the word is mum to anyone.
Mail service on the ship is well, whenever it is. When my son was deployed, which was more often than docked, it was usually when they had at sea replenishment.
I don't know where your son is stationed, so I can only use overseas, and basics from state side for what to send, and when. You can send a package at anytime, but if you know of a deployment and your son is overseas, send ASAP. That doesn't mean it gets to him ASAP, it may arrive after they have left, which in that case it will wait for the next replenishment. That replenishment can be in three days or two weeks.
Things that are OK to send would be water flavorings, they love those since the water on board is sea water run through a Light Weight Purification System. You can send candy, but no chocolate (it melts), most love things like cup of noodles, packaged meals that are in a container for microwaving, crackers, goldfish snacks, cookies, etc. Decks of cars, small hand held "toys" that are entertaining, but not expensive, Usually recommended if you are sending nuts of any kind that they are shelled. The shells can cause problems in certain areas. Small containers of toiletries, shampoo, toothpaste (even a new toothbrush)etc. Toiletries are available on board, but they do cost them money, and not much variety. One thing my son and his friends liked were what they call "Battle Rolls." LOL Those are the toilet paper you buy for camping, no center cardboard, and compact. On the ship, if a bathroom runs out of toilet paper is may be a while before it is refilled. Nothing like a trip to the bathroom and no toilet paper in it. I sent my son a supply of Battle Rolls right away. That way he always had some to pack when they left. He would shoot me a message saying "Battle Rolls depleted" when running out. Ha!
If he is overseas you do need to check the USPS international shipping for that country, and also look up prohibited items in that country. If he does live off base, never send anything to a street address overseas, always send it to his FPO, or APO address. When the mail is delivered to an FPO or APO the military has control, but the local country may also be there to inspect.
Now, not to say there aren't some things you can "get away with" sending, but do check it. Mail in other countries may be handled differently in each country. To Japan I could send almost anything, to Bahrain not so much. Google will be your friend if your son is overseas.
Does that answer some of your questions?
On Reddit, in the r/newtothenavy subreddit, there's a comprehensive set of lists from sailors on how to prepare for deployment. Very useful.