That isn't really a question that can be answered with what you have provided.
What you describe is insufficient to get a sense of the level of sophistication you are aiming for.
And why do you think you need a soundcard at all?
And it depends on exactly the output options are from your vinyl record player (old RCA only, newer laser vinyl player with digital out output options, etc... lots of possibilities)
For example, if you have an older record player, with only RCA output jacks (ie the red and white plugs), you may only need a USB dongle which converts the analog RCA audio output into USB audio for PC.
However, if you want to do some nice clean-up and tweaking of the audio you 'may' want the audio to route through either a physical audio mixer (if you wan to keep it old school) or route the audio via Audio editing software (or DAW) before getting to OBS Studio
Due to the nature of free/consumer livestreaming (heavy data compression), it is common to adjust the audio signal so that it sounds good for livestream audience. And beware, there is NO right answer/config. Folks listening on mobile device vs those listening thru typical HiFi system (proper speakers) are going to get a different experience. If you optimize for real speaker listening, mobile device users will have a sub-par experience, and vice-versa. a common approach is to tune for the majority of your listening audience, and leave it at that.
