Not really anything specific - just I'm a fan of anything that has been improved, generally encompasses most mods. Additional items, graphical improvements, UI enhancements, anything really. If it makes the game better, I'd download it.
Anyway, I'm not asking you to provide a mod list or anything, I was just curious if a STEP like pack existed, but it seems not.
OK, the next key question is whether or not you want to get into settlement building and if so whether or not you want to do it yourself, manage it yourself by defining zones for your settlers to build stuff in (e.g. "build accomodation here and here, build shops here and here") or whether you want it completely automated with your settlers scavving for resources to build entirely by themselves. That completely changes what mods would suit you best.
In general for modding, I recommend Nexus Mod Manager and the Nexus mod site in general. The site makes it easy to see if any mod clashes with any other mod, if any mod requires any other mod and to search for mods. The manager makes it easy to install and update mods. I also recommend LOOT, a seperate program which automatically sorts the load order for your mods. It's not always perfect, but even with 146 mods it has always been perfect for me. Install them in any order, run LOOT, job done.
For UI enhancements, I have two mods I rate as so good that they should have been part of the game from the start:
https://www.nexusmods.com/fallout4/mods/1235 Full Dialogue Interface. Displays dialogue in full. No more Yes/No/Question/Sarcasm nonsense. You can see what your character will actually say for each option.
https://www.nexusmods.com/fallout4/mods/3191 Screen Flicker Killer and no blur effect. Fixes the Pip-boy screen so it doesn't flicker, blur and jaggle with scan lines. Much better to use and realistic - it's an important item for your character, so of course they'd fix it as soon as possible.
Less important, but things I found made the game nicer to play:
https://www.nexusmods.com/fallout4/mods/1064 VATS Tweaks. I use it only to disable killcam and critical hit cam, but it has other functionality if you want it.
https://www.nexusmods.com/fallout4/mods/17632 Disable Headbob. Stops your viewpoint bobbing up and down as you move. In vanilla, it's bad enough to give some people motion sickness.
Almost all of the mods I have installed are for settlement building, so whether or not that's useful to you depends on what you want to do (or not do) with settlement building.
Additional items...are you after clothing, weapons, armour or secondary things like food? I have a few mods installed for each and one came out yesterday that adds something that was unrealistically missing from the commonwealth - bread.
I like this one:
https://www.nexusmods.com/fallout4/mods/4865 Custom Combat Armor. It allows you to convert between standard, sturdy and heavy combat armour and to customise the appearance of each part by adding paint, decals and/or material effects (e.g. very shiny pieces, like they were chrome plated). However, the current version requires another mod:
https://www.nexusmods.com/fallout4/mods/6091 Armor and Weapons Keywords Community Resource. It's probably a good idea to install this if you are planning on installing some armour and/or weapons mods. Some such mods require this mod, some will use it if it's available. Essentially, it's a framework for menus and keywords for armour and weapons so that different modders can more easily ensure that their mods don't clash and so that similar items from different modders appear in the same menu in crafting. I don't use it, but I probably would if my modding wasn't so heavily focused on settlement building.
If it's clothing you're after and you don't want eleventy thousand mods of hardly any clothing for women with very large breasts, this one is my favourite:
https://www.nexusmods.com/fallout4/mods/28629 Retro Fashion Overhaul. A bunch of stylish clothing based on real world 1930s clothing.
I also like this one, which contains lots of clothing despite the name:
https://www.nexusmods.com/fallout4/mods/22431 Eli's Armour Compendium. It adds a new location - a clothing shop. As well as buying clothing, you can buy the patterns for making the clothing yourself. Lots of clothing. Not just the usual stuff either - you can make hats, scarves, bags, all sorts of things.
That's something for you to be going on with.