-I'm Verizon with unlimited but I believe the cheapest plan is $20 for only 2GB(not enough for me). If you already have a data plan it's $10 more to add another device. Sprint is still offering unlimited, but I don't know their pricing anymore but I haven't heard of a Sprint version. I've only seen the verizon one.
-The new version only adds 4G otherwise it's identical, but I'm wonder what the battery life with 4G turned on. It has the same battery as the wifi version.
-All the apps I mentioned are pressure sensitive, including PS Touch. There are a lot more pressure sensitive drawing apps but these are definitely the best of the bunch.
-Rooting is not hard as long as you carefully follow instructions. There is a chance you can brick your device where it would just be a paper weight. I would only root if I wanted to use a particular that needed root., or the reason of space that I mentioned earlier.
-The problem with any laptop/tablet is that it takes a while to boot up and shut down, unless you have it on standby which still decreases the battery time by a lot. Plus they tend to be a bit bulkier. I used to use a laptop with a wacom that would attach to the keyboard with velcro, but I could not use it while, for instance waiting in a store for my girlfriend to finish shopping. With a straight tablet I can whip it out and sketch while walking. Plus I didn't want to carry a $1000+ piece of hardware around. The chances of you dropping it, forgetting it, getting it wet, or having it stolen is pretty high if you carry it around everywhere. Also the battery on tabs last a lot longer. My laptop with continuous use was 2hrs. I had to carry a spare battery with me. My Note 10.1 lasts longer than I use it in any given day as long as it is fully charged in the morning.
Honestly if your just using it for sketching a full version of Photoshop, Sketchbook or any other program is way more than you need. You want it to be quick to pull out and use like a pad of paper.
Another thing you might want to look into is Splashtop HD. It's a remote desktop app that let you control your desktop remotely. I haven't been able to get it to work on my tablet yet.
I have used Splashtop 2 to use my Note 10.1 to control Photoshop, but that only works when connected to the same wifi network. It worked well and you still get pressure sensitivity with very little lag, at least with my sketching speed. I did have an issue because I have a triple monitor desktop setup with palettes on one of the side monitors. I had to create a special workspace in Photoshop with all the palettes on one screen because switching screens remotely is a pain.
I don't know how it will perform over 3 or 4G with Splashtop HD. Maybe someone else who got it to work can test how well it works with Photoshop.
On a side note there is a way to add almost any app to multi-view. You don't even have to be rooted. I mention this because I use it to float reference pics on top of PS Touch.
Non root method
[Tool] Add Multiwindow-option to almost every apk files - xda-developers / Rooted method
[APP] MultiWindow Manager 1.2.7 - xda-developers
The advantage of the rooted method is that the apps that you add to multi view still get updated. With the non-root method you have to run the new version of the app through the process again and re-install.
PS Touch only works in landscape(not sure why) but I have an app called GMD Smart Rotate which forces PS Touch into portrait. All the other drawing apps mentioned work in both portrait and landscape.
Not too long ago I had the same decision that you are making now, and was looking into the same options that you are. In the end I'm very happy with my choice. Good luck.