Well if you are apprehensive about mods making the game too difficult for you before you get better then you could just get SH3 Commander. Its a seperate program that allows you to manage your profiles and create them from a seperate program. You can modify many options for the game here that are otherwise unchangeable in game and can even choose which type of sub and which month you want to start in.
It is true that GWX and NYGM both create significant changes towards realism. However you might want to also give the War Ace Campaign a look. Its pinned in the SH3 Mod Workshop. I've never played it myself but from what I've read it is basically an eye candy mod that gives you most of the pretty stuff thats been developed but it mostly doesn't change the stock game play dynamics.
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