Longer answer: This game is a journey, not really a destination. If you're looking for a traditional 'endgame', it's pretty much everything you've already done, only more of it. Avenues to the 'best' gear open up fully at 80, as well as all the options your class affords in terms of its trait lines. Beyond that, it's about what you enjoy doing and the things you want to have.
Well, other than character slots, most things purchased from the Gem Store are cosmetic or convenience items. So you needn't worry about having to spend RL cash on the game. It's entirely possible to get them with in-game gold as well, just save it up, try and watch the market for when gem prices go down and buy them when they're lower. Also watch for when things go on sale in the gem store to save further, if possible.
There's plenty to do by yourself, and if you prefer a more social group-style experience, join a guild and see how that works for you. A good one will have people willing to help you out as well as things organized for guild members to take part in. Remember, that should be a two-way street. Give help and you'll get it in return.
My advice is to explore the world, check out all the starting areas, play around some with your personal story, try the Living World content if you care to, and just jump in and play anything that sounds fun to you.