The SH4 v1.4 limits the mods available for your use. If I'm remembering correctly, Sniper297 still uses v1.4 quite a bit, and may have more info than I do. I'm also not too sure about how many mods for v1.4 there are on the SubSim site... You might have to go on a web hunt for some of them. I do not have links for most of what's below...
Trigger Maru Overhauled (TMO) is probably the most "famous" mod, and I ~think~ it was v1.7 that was the last version that ran on v1.4. There's a "patch" for that also.
Run Silent Run Deep Campaign (RSRDC) v350 (??), and it's associated TMO & RFB versions and patches...
Real Fleet Boats stayed with the "v1.4" designation with the game's version number. There was a "fix" patch for it...
And there's TMOwTw, which is TMO with Training wheels, which I think followed the TMO number sequencing...
There isn't a GFO (Game Fixes Only) mod for v1.4, but you could string a lot of
Webster's mods that are compatible with v1.4 together and make a sort-of one... That link is for a Search on "Webster", so there are hits on mods that aren't his. Read.
... And I'm sort of partial to Fall of the Rising Sun. I cannot find the earlier version that is in the English language and compatible with v1.4 Silent Hunter, but I'm thinking it was v1.1 that had a couple of versions. Versions 1.2 and 1.3 were for SH4 v1.5 UBM, then they went back to Silent Hunter v1.4 with Fall of the Rising Sun v2.0. It is beautiful to look at, and tougher than TMO to play. Its only language is German. If you can deal with that, it is really a cool game. It will crash on you though at times.
Beyond that, I do recommend that you get yourself a copy of the "Add-On" U-Boats Missions (usually about $10US), which is v1.5, preferably a disk, but the download sites work fine, other than don't get the Steam version unless you have the Steam version of the "base" game. You can keep a separate SH4 v1.4 install in one folder, and update another install to v1.5 until you get used to it, but using the v1.5 opens the use of all the newer mods to you, some of which are still being developed and tweaked, such as
Fall of the Rising Sun Ultimate,
Ralles RealModSoup, besides what Bubblehead1980 is working on... to top all that off, keltos01 is working on a
Japanese Campaign where a person can drive Japanese submarines basically around the world. That cannot be done in v1.4...
And really, a person should acquaint themself with
Rockin Robbins' Silent Hunter 4 Corruption Management System,
MultiSH4 v1.5 and
CapnScurvy's Windows10; Large Address Aware; SH4 Install write-up. All basically "mandatory" with today's modern computer systems...