Would the CLP's speakers be sufficient? If not what type do you recommend?
I also will probably need a good sound card recommendation.
How picky are you about sound quality. The more educated your ears are the more harm it will do to the back account.
I assume you are buying the software virtual instrument because you think it is better than what is built into the CLP. So you are looking for a quality that is all around better than the CLP. If so then you are not longer in the world of "computer speakers and sound cards" but are into pro audio and studio gear.
When we get to this level we refer to a "sound card" as an "audio interface". They are not hard to buy. Just shop in the "correct" store. Find one that caters to musicians and recording engineers. If you will ONLY be recording one digital piano you don't need much and $200 is more then enough budget for an audio interface. But it you want to also record a vocalist and a few other instruments, in other words four or eight tracks at once it gets expensive and you will need microphones and mic preamps and so on. But for your use two channels in enough and you don't need to mic a digital piano.
Here are a few USB audio interfaces to look at all are top brands $80-$180
PreSonus AudioBox USB
E-MU 0202 USB 2.0
You will also need some software for recording, mixing and mastering. I use "Logic" but there are others.
Speakers are another issue. If the goal is better than CLP sound at the volume level and power of a real full size acoustic grand piano you are looking at maybe $1K, give or take a factor of two. If you want high quality sound for just one person buy headphones for about $200 (I like my AKG K240 headphones) If the CLP sound is "good enough" then buy a cable and plug the audio interface in to the CLP speakers via the Line In jacks.
When buying speakers you have the choise of powered studio monitors or pasive home streo type speakers with an amp. There is a difference in the sound and you really have to listen carefully.