I agree with you. And I disagree.
The inventory/bag system is terrible. SkyUI improves it a lot. But even then, it's still not good. I agree that bag-system like we see in MMOs would be a lot better. Morrowind had such a system. I loved that. I don't understand why we can't have it in Skyrim too. (Ok, because of controles on consoles probably). in Skyrim, the GUI is build with special software, not with the Construction kit. So it seems hard to redo the GUI.
The keybinds and favorites system is also rubbish. Lots of bugs. But also the basic design is a pita. If you change certain keybinds (F, T, tab) other functionality stops working. I had changed all my keybinds. I couldn't recharge my enchants. I couldn't rename enchanted items. I couldn't use tab to get back in the menu-structure. It was terrible. Clicking "reset" didn't work. When I reinstalled my game at some point, I never touched the keybinds, and now stuff kinda works as it should. Which is still not good.
I agree with you, OP. Skryim should have a system with actionbars. Put any action, spell or item in an actionbar slot. Bind any key you want to any actionbar slot. Just like MMOs do. That would make keybinds so much easier. I do think actionbars themselves should be hidden. And only show themselves during configuration mode. I love how minimalistic the GUI is during regular gameplay.
I disagree about the targeting system. I like how Skyrim does it now. I really dislike the "targetting" of enemies. Having a big colored circle underneath them. Again, I love minimalistic GUIs. I play a melee character, without a bow even. Yes, aiming at an enemy might not be easy. But still I think it's more fun than the auto-aimbotting of MMOs. But if you want a "tab" auto-target key, I think that should be doable. It should just make your character turn towards an enemy. And hitting it again should turn you to the next.
About movement and aiming. I think you should just get used to it. It will take a while. But everybody can learn it. I'm an old guy.

I started playing games (in the nineties) when I was already older than most people on these forums. Still I could learn it. (I must say, I play with a trackball and keyboard. Done that for years. Even played FPS games with that setup. Because I find a joystick (with lots of buttons) much more convenient than a keyboard). Skyrim could add keys for turning. But then, you still have to move your aim up and down. So you would need 4 extra buttons just for aiming. I think if you got what you asked for, you might not like it as much as you think.
You ask for spells/action to not be bound to the mouse. I assume you mean: using your right hand and left hand ? Those can be bound to other keys. I use Y for right hand, and left-mouse for left-hand. It works. I haven't had any problems with it. I assume you will be able to rebind both functions if you want. Try it.
If you get seasick by turning with the mouse, try changing your mouse settings. In game, and in the control panel. Slow down reaction speed of your mouse. Turn of acceleration in the game, see if it helps. Personally I prefer a trackball (Logitech Marblemouse, it's symmetrical, so it works in the left-hand too).
But reality is: Bethesda will not change any of this. They made these design decisions years ago. They stuck with it. They think this is best for their average customer. Even if they come to realize they were wrong, they will not change it. Just because Bethesda never changes anything after release. We are already surprised and happy they did fix quite a few things in the last months. Personally I hadn't expected them to release a patch with the compiler-settings-optimization. It amazed me they acknowledged they messed up big time there, and fixed it. But they will never come back and change major design decisions, like their GUI. If you want something changed, you have to rely on user-made mods, on tweaking your own PC, and use your own wits to get an acceptable GUI. Sorry.