I thought that I recognized the name, Welcome back.
The first thing to know about
Prepar3d V4 is that
V4 is far less compatible with
FSX than
V3 was.
If you've already started installing FSX scenery you've may have noticed that already - Prepar3d V3 won't start.It's a little more forgiving of aircraft
IF you install them to a folder, and then manually copy them into P3d V4.
In all, it'll be a bit worse than going from
FS9 to
FSX was, especially with FSX scenery.
One exception to that is
Blue Sky Scenery. Even then, manually place it in
P3d V4.
I hate to send you off to another site, but you
REALLY,
REALLY,
REALLY need to read some of the posts on AVSIM, starting with this one -
Prepar3D v3 & v4 video Tutorials.
The videos are short and to the point. They will save you a great deal of time, and help you recover
P3d V4 when you go too far.
Other than that, I wouldn't trade P3d V4 for anything.
(Except, maybe V5 
)One piece of scenery that I bought for FSX was
New York City X.
The scenery is incredible detailed. Unfortunately, even with all of the sliders far to the left it would crash FSX within minutes.
Now, with P3d V4, I have most of the sliders to the right and can fly it as long as I want without crashing to the desktop.
There is a mad dash to produce, or convert, software for
V4. Some is already out, but some, I think, will never be made compatible.
We're in the early days yet, so be careful what you buy. And, again, the wrong scenery will probably crash
V4. That AVSIM link will help you to recover, often without the need for a full re-install. Trust me, I've already done it a few times.
The wrong aircraft will crash
V4 too, but
(so far) it's easier to recover, just remove the aircraft. Basically, If it doesn't have an picture when you go to select it, DON'T try to use it.
As to the weather I switched from OpusFSI to
Active Sky for P3Dv4 (open Beta). Your choice of cloud textures is up to you.
As to the choice of scenery, it comes with a basic version of Orbx Global. Other choices are becoming available, but I've been hooked on Orbx for the past couple of years and couldn't give you an unbiased view.
Is it good?
Absolutely!This is Prepar3d V3 with Orbx scenery.
And this is the BASIC Prepar3d V4 scenery of the same area.
You've come back into flight sims at the right time. 
