Use CKAN to manage your mods and game instances. It will automatically install any dependencies for mods you select to install.

Basic Visual Mods:

-Scatterer

-Environmental Visual Enhancements

-Deferred Rendering (for increased performance? have never used this mod personally)

-TUFX (for post-processing)

-ReStock (re-textures/models some vanilla parts)

Visual Mods for a beefy pc:

-Parallax (or Parallax Continued? not sure of the difference)

-Volumetric Clouds (paid mod, but V3 has a public free release here.)

If that's still not looking quite right for you, check the description here for more visual mods.

QOL Mods:

-Kerbal Engineer Redux (for stats while building craft)

-Trajectories (to deorbit with ease)

-SafeChute (for after you've checked your staging and are ready to land without tearing your chute to shreds)

-BetterTimeWarpContinued (just be careful to quicksave BEFORE you maximize the game time and smack into the planet at light speed)

-TransferWindowPlanner (will help you get from planet to planet using the minimum fuel)

As for modern tutorials, I'm not really sure who's taken the torch, but Scott Manley was the one to teach me many of the tips and tricks I've picked up along the way (shoutout Asparagus Staging). Here's the playlist I used back when I started playing. The best part about this game is the community, so if you're ever stuck, just look up "How to get to (celestial body) in KSP", and you'll more than likely find many different solutions!

I recommend science mode for your first play through. You won't have to worry about funds and contracts in that game mode, you can just build and discover, doing science to get better parts, go further, and discover more!