There are no "original" manuscripts, but many early manuscripts, dating as early as 100 AD. (Well a tiny piece of one- The Rylands Papyrus)
There is a huge science of comparing manuscripts, copiest errors, and transcribing mistakes. They have been traced on all 5000 extant copies. So there is a good knowledge of how the New Testament was written in the Greek.
While KJV used much later manscripts, because the earlier ones had not yet been discovered, the current translations use the earliest and most reliable Greek manuscripts.
If you study and translate the Greek, you will find that even though there are some language differences, it is more about a translator picking one English word over another for the Greek. But basically, the meanings are pretty much the same.
Some versions are more word for word, like KJV, ESV and NASB for example. Some are paraphrases, like the Message or The Living Bible. In between, there are thought for thought versions, like NIV, Holman's and NAS.
Learning the original languages are the best way to go, if you are really concerned about translational issues. But don't just use Strong's, instead take a few courses and actually learn the language, grammar and syntax, not just isolated words.