Rob, it sounds like you are quite new at a lot of this. I don't say that critically, it was true for all of us and there are still many (many!) things where I still feel quite ignorant.
But, it sounds like you are making (or have already made) some very significant and expensive decisions without having a lot of the fundamental knowledge. If you haven't already made those decisions, I respectfully suggest that you might want to hold off a bit and get that grounding knowledge. Then, you'll have much more confidence in the decisions you are making and knowing they are right, for you.
Along with the above, I'll give you this piece of
advice: When it comes to boats and
boating, there really is such a thing as good seamanship and bad seamanship. The differences have evolved over many generations of sailors (often in a ruthlessly Darwinian way, I might add. The ocean is a beautiful mistress, but totally unforgiving. You might get away with bad seamanship for quite awhile, but she will, eventually, always balance the
books.) Getting
training, whether from a formal "school" or via friends and
books, is highly recommended. Always better to have the
experience of "oh, I remember that and I know what to do about it", than "oh, crap! What's going on? What do I do?"
As far as boats are concerned, there is an amazing variety and that's one of the wonderful things about them. There are lots of "right" ways to go about achieving a good boat that does what you want it to do, and well. Sometimes you will hear a certain boat or method as being the "correct" way with the inference that all others are not. Almost always, that is opinion masked as fact. The trick is knowing enough so that you can figure out what's right,
for you! Believe me, they are ALL compromises, your job is to figure out the set of compromises you are willing to make.
To answer your specific questions:
Yes, there are cockpit enclosures available, or can be made, for just about all boats. For Lagoons, specifically, the factory makes enclosures, but others have them made. I have no knowledge as to the quality of the factory enclosures, but I'm sure someone on this thread will.
Is
GPS worth anything? Yes, definitely. You're going need to learn
navigation and
GPS is an important part of this. Do NOT, though, let it be the only part!
Charts, chartplotters, GPS, all of that stuff can be both wrong and unreliable.
Learning traditional
navigation methods can look pretty intimidating at first, but this is where a good class makes it both easy and fun.
Sat Phones? Very handy, especially for open ocean
communications. Not necessary, though. Some are better than others, do your research!
TV/Internet? Luxury items. Got the bucks and want to spend them? They are quite expensive, especially when you get more than a few miles
offshore.
Watermakers? Most boats do not come "standard" from the factory with a
watermaker. Almost all manufacturers will offer them as an option. Again, there's lots of variety in these things. You don't want to get stuck with one that doesn't meet your needs.
Hope this helps.
ID