A few tips:
In the Gulf Coast climate, cuddies are good for almost nothing but junk storage. Get a T-top or a bimini top. Some people still like them though, but I wouldn't recommend one for a first time owner.
Boats are like T-shirts. They shrink when you get them wet. Thing is HUGE sitting in your driveway, but when you get it in the water it's about half that size!
Whether buying new or used, pay a LOT of attention to the trailer. Most dealers get the price down by putting crappy, under-rated trailers under the boats they sell. Buy a boat with an under-rated trailer and you
will regret it.... I promise. Especially on long tows like it appears you plan on doing at least some of.
Boats are a maintenance nightmare. If you aren't handy with tools etc, find a fishing buddy who is.

Be prepared to spend lots of time cleaning and fixing little things. You'll be amazed at how much crap can break while it's just sitting in your driveway. i.e. My boat sat for about 30 days since last trip. (bad year). Took it out knowing that everything was working great. Baitwell pump went out in the middle of the trip, florescent light under T-top went out, the all around nav light bulb burned out, and the freshwater pump is now toast. All that stuff was working just fine on the last trip! Top that off with one of the trailer tires suffering a seperated tread. None of this stuff is serious and it doesn't take a genius to fix any of it, but it can be a royal PITA sometimes. It can also nickel and dime you to death!
My suggestion for a first time boat buyer in the south who wants to fish saltwater would be a 18-21' bayboat. Excellent all around boat that will fish the coast well, allow you to venture a few miles offshore in good weather and even work well for skiing and just plain old boat riding. Every boat design out there is a compromise. You always give up one feature or ability for another. Bay boats are the ultimate compromise boat. IMO, they don't do any one thing extrodinarily well, but they do many things plenty well enough. A T-top might be pushing it on a 21' bayboat, but a bimini that you can fold out of the way when you need to will work great. A personal opinion of mine. Seats in the bow of a boat are friggin useless unless you have your own private lake. Take it to a river with other boats and no one will want to sit up there due to other boat wakes. Same in a lake. On the coast, in bays etc, the bow is the last place you will want to sit unless it is a dead calm day and there's nobody else on the water. Worse yet, if you are fishing, those seats are ALWAYS in the way.
Become a weather expert. Boating is great fun and I wouldn't trade it for any other hobby out there, but a fishing trip to the coast in bad weather is NOT my idea of fun...and your son and wife won't appreciate it either. Doing a fishing trip is an incredible amount of work and expense. Make each one count. Bad weather includes sunny days that are too windy (on the Gulf Coast). If the wind forecast for the coast is more than 10 knots, I'll stay home and knock out some Honey-do's.
Boat shows! Excellent way to check out all kinds and brands of boats w/o driving all over creation. Even if you aren't buying new, just looking at and crawling around in the boats is very educational. You can also "shop" in realative peace as the salesmen at boatshows are usually overwhelmed by the sheer number of people and won't attack you as soon as you walk up...usually.
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Buy used. As a first timer, you probably won't keep the boat very long before you will want to move up or sideways. Taking the resale hit from a new boat is gonna hurt. Determine the type and brand(s) of boats you are interested in and start watching the classified adds. News paper and especially sites like this one and boattrader. Educate yourself on going prices for what you want. If you don't have a clue what they are selling for, how do you know if it's a deal or a steal? Start looking now. Even if you don't plan on buying for a couple of years. Go kick some tires too. This will help give you an idea of the what boats have been well maintained and which ones are just a disaster looking for new victim.
Before buying, I would have any prospects looked over by a mechanic at a minimum.
Ask questions here and other forums. There are no dumb questions.
Good luck.