Okay. I just realized I tend to replay games I really enjoy (especially deep rpgs), so I've decided that I'm going to beat G2 vanilla without NotR.

How can I install it without NotR, or can I make a non-NotR game, or how do I do this conveniently?

Note that saves aren't compatible between vanilla and NotR so you'll have to start a new game to go from one to the other in either direction.

Also note that NotR while it is hard and can be really frustrating in chapter one, it adds great story elements to the game. Without it the game really feels incomplete. Having a hard time early on is kind of worth it. Also remember that there is no need to face every hostile monster early on. They will still be there when you come back.

I'm pretty much aware of this... it just seems like I can't do anything right, I can't hit enemies consistently and the few NPCs I fight are so ridiculous that I really have little idea how I'm expected to do anything (talking of the beat 3/5 of Sylvio's followers mission).

I must admit I'm not a fan of the melee system in G2, it makes most of my attacks do a base minimum damage : /

Melee will feel very difficult in G2 until you get a good feel for the timing, at which point you starting kicking ass and taking names. As for Sylvio's followers, most of them should be pretty easy to take down as long as you keep your timing right (of course, if you just try to trade blows then all of them will put you on the ground in a couple of seconds). The only one that can be a real pain is Bullco, since he has a high enough weapon skill to mix in some extra attacks that really screw with the typical timing for fighting humanoid opponents.

I beat Sentenza too:
Ice Block + Melee until spell wore off - run towards the cave with field raiders - climb that rock - melee again.

Works every time.