I use Cubase so I'm not familiar with where the buttons and knobs are on Reaper, but all DAWs have the same basic functionality. With that said, one thing you'll want to consider is the difference in your DAW between "sends" and "inserts."
An insert can be thought of like a traditional stomp box in front of an amplifier. Your guitar cord goes from guitar into the stomp box, then out of the stomp box into the amp. Thus, it is "inserted" into the guitar signal path.
A send is more like parallel processing. Imagine if your guitar cord went from your guitar and then was split with a Y adapter. One side went into channel one of your amp, and the other side went into channel two. If channel one is your actual guitar tone and channel two was your effect, you could turn the volume of your effect up and down without affecting what's going on with the unaffected tone in channel one. You'd just be mixing in how much of the effect you wanted, to blend it with the unaffected tone.
Back in the DAW, inserts are often used for something like compression, where you don't want to preserve the tone that went into the insert, all you care about is the end result that happens after the effect. On the other hand, reverb is commonly used on a send bus. For instance, you have a singer's vocal track, and then you "mix in" the amount of reverb that you want.
Also, while an insert affects one and only one track, a send bus can be shared by multiple tracks. Using our vocal example, you could have four singers on four tracks. They might be EQ'd differently, but they could all mix in some reverb from the single reverb send. And each singer could mix in different amounts of 'verb if you like.
Now, back to the Kemper. To turn off effects, just press the buttons to turn off stomp boxes, reverb and delay. Now you're tracking just your unaffected guitar tone. Let's say you record it on track one.
In your DAW, you'll want to create a send bus since they're time based effects. (There are ways to do this as an insert but I'm showing the most common use case). Once you have the send bus created, then you select an Eventide effect for that bus. Now go to your guitar track, enable that send, and turn up the volume of the send bus until it's the level you like, thus "mixing in" the effect.
If you want to use more than one Eventide plugin at the same time, simply create additional send busses, e.g. if you want a chorus, a flanger, a delay and a reverb, create four send busses and select each effect into a different bus. Now, on track one where your guitar part is, enable all four sends and mix each one to taste.
As I mentioned, since I don't use Reaper I can't tell you the specifics of how to do this in that environment but it absolutely has these capabilities. Depending on your preferred method of learning, you can either RTFM or search YouTube for "create send bus in Reaper." It's not difficult to do, it's just a matter of getting familiar with it.
Hope this helps!
Thank you VERY much!