First of all, DO NOT do this in Premiere, or any other NLE.
It is slow, and your methods of exporting / reformatting / checking are limited.
Now, Captions (or Closed Caption) are generally for the deaf and hard hearing. So, not only is the dialogue written, important sound effects is also noted. The position and color of the captions indicate the speaker.
You can turn them on / off, the information is send with the video, and the TV sets overlays them.
Due to backwards compatibility, they are still ugly, have very limited space (as you have noticed) and then there is the problem that you need to know the load time to be sure they will appear. (Long technical story.)
To preview captions in Premiere, you need a card that supports that, and a monitor that supports that, and they have to be turned on. Can be a hassle, and as stated earlier, they need load time, so they don’t always appear when you jump around.
Subtitles are just to translate the spoken content. They are generally white, and have no more than two lines.
They are NOT always burned in. It depends on the broadcaster.
Most of the time you have to supply a separate file to the broadcaster, who will add the subtitles on the fly while broadcasting. (So your master is clean, but the end user receives them burned in.)
But eg Netflix sends them as metadata, and the Netflix player will overlay them if the end user turns them on.
Then you have to learn about timing / read speed. You cannot simply translate everything and put it on screen.
(It will be too much to read in too little time.)
Depending on the languages, you need to shorten the text by 1/3 on average. That is often a challenge, and you end up re-writing parts of the text / re-arranging sentences. (People have tendency to talk very sloppy, if you read subtitles without the movie it always looks weird.)
This is hard work, and you will be doing a lot of revisiting.
Now, a feature film easily has 1000 subtitles. So you need a way or creating them that is fast.
I strongly suggest using a dedicated editor, and I recommend this:
https://www.videotoolshed.com/product/subbits-subtitler/
(But that might have to do with the fact that I’m the creator of the software.)
Bouke
http://www.videotoolshed.com