SFxT still uses the discontinued "Games For Windows Live" service. IT IS REQUIRED EVEN THOUGH IT NO LONGER FUNCTIONS.
That means you CANNOT PLAY THIS GAME ONLINE. Furthermore, if you just want to play Arcade or local multiplayer, you're going to have all kinds of issues. You can't save your progress AT ALL if you're not logged into Live, and your DLC purchases will not show up either (though you can activate them each time you play by going to the in-game Store and redownloading everything).
The PC version is also missing the Swap costumes for the 12 DLC characters, so the "Complete Pack" Swap DLC is a bit misleading. These characters have Swap costumes in the console versions so they DO exist.
The game was originally released under a crushing amount of controversy which highlighted Capcom's extremely greedy and damaging monetization strategy. They chopped up bits and pieces of the games (characters, gems, features, customization, etc.) and then resold them individually at a ridiculous premium. You can get everything for the price of a full retail title now, but when the game first launched it would have cost you upwards of $150.
For all of these reasons and more, SFxT never really took off, so 1) even if you could get online you'd mostly be playing against laggy hardcore Japanese players, and 2) don't expect any meaningful support for this game from Capcom.
Lastly, I will say that--as more of a Tekken fan--this game was conceptually a dream come true. The execution is mixed, as you can probably tell by now, but there are a LOT of characters to play around with and the Tekken crew was pretty convincingly converted to Street Fighter-style gameplay.