Load her up and update immediately to patch 1.4. Decide whether you want to buy the U-Boat Missions now or later

. Then I'd say play the game for a couple orf weeks with no mods at all. Unless you know what your starting point is, how can you tell if you like a mod or not?
Then the major mods are:
Trigger Maru Overhauled: changes much about the game. Incorporates Run Silent Run Deep historical enemy traffic, changes the nav map so it doesn't give you too much information like different shapes for different types of ships, different colors for friendly, neutral and enemy. It tries pretty successfully to give you the information a plotting crew would give you. It beefs up the sensors of the enemy escorts so that they are more difficult than the stock game, making survival a challenge. TMO is formulated to produce more challenging game play, resulting in historically accurate player behavior. Ducimus is the mod wizard for this one. Please curse at his evil airplanes for me.
Real Fleet Boat: This mod tries to replicate the real life capabilities of everything. If the Japanese didn't sink very many U-Boats, you will be quite safe from their attacks, maybe even safer than stock. Torpedoes have minds of their own, just like in real life, and you may find yourself using some period authentic curse words as you hope for one that works properly. This is a new team working on RFB, so look for even greater things in the future. Their new real deck gun is an absolute masterpiece. Swdw is leader of that team of geniuses.
Run Silent Run Deep: is strictly concerned with enemy traffic. Lurker_hlb3 is the insane person behind this one. Why do I say insane? Every single Japanese ship is on a historical course. There is no random shipping, just actual traffic as logged on official sources. THAT is amazing.
Pacific Envronment: Mod by the Reflections on the Water team, headed up by kriller2, changes sea behavior, light reflections, sky effects, just about everything environmental for amazing realism! This mod turned the Silent Hunter world upside down.
Really Environmental 4.0: by W_clear is a new environmental mod from Germany that is an alternative to Pacific Environment. I don't know much about it other than the orgasmic endorsements of it in its thread and that Ducimus has adopted it into the Trigger Maru mod. I believe that means that if you have TMO, you don't have to install this and PE would be redundant.
OK, everybody can throw things at me for all I left out or didn't get quite right. I'm tough. I can take it. And I'm using Water boy as a human shield.