Welcome! Now keep in mind these are personal opinions
The game population has gone down over the years, as it will for just about any game, but honestly I don't think it has gone down any less in the past 3 years or so. A lot of people play as froobs, then upgrade to a cheap sloob account (access to Shadowlands for I think $5 a month) when they feel they want to experience more of the game.
That said, you don't need SL or any of the other expansions to have a good game experience. A lot of players with all of the expansions will still spend a good portion of their time on Rubi-Ka and some prefer it because SL can be a super easy leveling route if done right and people don't learn the ins and outs of the game or of their professions very well. This causes issues at end game when they don't know how their toon works properly and they get frustrated and complain about it.
I have a toon that I level solely on RK just because it can really be fun. Having perks from SL and AI, plus Research from LE do help a lot, but they aren't requirements and I think not having them can make someone a much better player.
Back to the population, a lot of people have been rolling new toons lately and starting froob accounts, so finding people to help you at low levels really shouldn't be an issue (considering the game is supposedly dead, there are a lot of new characters running around).
The 10th anniversary of the game is also coming up soon, which should be a lot of fun. A ton of things are in the works for the game really, profession changes, a new graphics engine, a lot of updating to game icons and such via the players. It's really not as stagnant as people would like to believe.
As for money.. that's a real pain. Even for me, and I've been around since 2001. Starting a new character can be a real process and can try your patience, but a lot of the fun is learning. Just about every mob drops armor of some kind and you get to piece them together how you want. If you fight a lot of mobs that attack with chemical, you can get a set of flowers armor together (pretty sure that's the chem one lol) and the same for just about anything. When you get in to SL and the others you can get pigeon holed in to specific armors, something you'll never have a problem with as a froob.
I say give the game a shot. We have a ton of guides and other resources here that will keep you out of the dark and always having things to do, and if you really do end up not liking it, you won't have given up that much time and no money as a froob.
Hope that helps