You can find the Follower Mod here (it's the most basic and functional I could find. Literally just Follow, Go Away and Open Inventory):  

Sharing and Caring Companions at Fallout 4 Nexus
Recommend: SCDC - Subjective Cinematic Dialogue Camera as the player has no voice / animations in FoLon for the hire / fire companion scenes.

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Just a quick and dirty tutorial about how to install Fallout London without messing up your modded fallout 4 install. 

This guide assumes you have a Fully functioning "old gen" (1.10.163) install of Fallout 4 with F4SE v0.6.23 installed properly. You'll need Mod Organizer 2 if you don't already have it. You can run both Mo2 and Vortex on the same computer for the same game. 

Obviously you're going to need the Fallout London mod, go grab it for free at GoG.



Don't bother with the galaxy installer, just download all the loose files



While those are downloading, Open Mo2 and create a new instance (File > Manage Instances > Create new instance)



Just pick global..



For Fallout 4...



Give your instance a name (if asked to configure, tick both "Use profile specific (game INI files & Save games)" Archive invalidation should be ticked as well.



Good to go, you can close Mo2 for now.



Click the Setup exe in the files you downloaded



Change the "Options" BEFORE hitting install



"Install" it in the /mods/ folder of the Mo2 instance you created earlier



Hit Exit when done (it's not a full game and wouldn't launch even if you tried to)



Go to your /mods/ folder and delete *everything* here except these 3 folders (src should be a duplicate of the f4se files you already have in your Fallout 4 folder)



Open Mo2 and tada! Fallout London (aka. Data) mostly installed 
Note: DlcBlock.esp should be moved to below LondonWorldSpace (the next few steps will fix this).



Maybe rename the mod "Data" to something more Fallout Londony



Copy (and replace) the 2 files from ../Mo2/Fallout London/mods/__Config/  into ../Mo2/Fallout London/Profiles/Default/



Do the same with the 4 files found in __AppData/ (there are a handful of lines necessary to run London not found in the default files in these files)



/Profiles/default should look something like...



Once the loose files are copied over to /profiles you can delete these, or don't.. Just be sure you don't enable them in Mo2



Click on the little drivers license (aka profiles) icon in Mo2



Be sure "use profile specific saves" is checked. Use profile inis should be checked by default. 
That is, if you don't want your London and Fo4 saves and settings to intermingle.



Launch Fallout London using F4SE from within Mo2 and...



Quit Fallout London, select file > manage instances, and double click Fallout 4...



And we're back to good ol Fo4, fully modded and untouched by Fallout London.



This presentation brought to you by Vim! "Healthy doesn't even begin to describe it!"

UhuruNUru made an excellent point. Once everything is up and running open /mo2/falloutlondon/mods/falloutlondon/, select *everything* (/f4se/ to vivid.txt) and right click > "Add to FalloutLondon.zip". Move this zip archive elsewhere for later, to downloads for instance. You now have a standard zip mod similar to those found on the nexus.

Remember to backup your profile files as well.