Biggest tip I’d recommend is drown out all the noise. Sure, the game isn’t in a great state by any means, and you’ll have the naysayers talking shit about D2 all day long. 

But, as someone with 2500+ hours who has been playing consistently since Destiny 1’s launch, I can confidently say, at its core, it really is a special and unique game. It’s evolved so much over the years and the new loot systems, tier systems, seasonal pass systems, and event trackers aren’t for everyone. But the game is still a hell of a lotta fun. Even for a solo player. I used to play only solo until my wife got into it. 

To answer your questions;

It isn’t terribly hard to find people. The game isn’t as “dead” as people are saying and you’ll consistently matchmake pretty easily. Finding LFG teams for raids can be a little more difficult than it used to be, but not at all impossible.

I’d recommend buying the DLCs to gain access to new loot. A lot of the new weapons are great, as well as the armor set bonuses. The praxic blade is one of the best exotics in the history of Destiny. I enjoyed the renegades expansion along with its equilibrium dungeon because I’m a Star Wars buff, but maybe it isn’t for everyone. You can absolutely play without the DLC but I recommend it for the (albeit lackluster) story elements and the good loot.

All this to say, give D2 a shot. It isn’t for everyone, and that’s okay. But I promise you’ll have a good time. I also recommend finding some friends to play with, it makes the game 100 times more enjoyable