The KJV is still a good English translation. It's been around for hundreds of years and has been tested. There are more English bible references, tools, etc., that use it for running text than
any other English translation. Despite the inclusion of some archaic usage, the KJV follows the original languages very closely (i.e., more "word for word" than "thought for thought"), enabling you to better understand the connection between the underlying Greek/Hebrew and the translator's choice of diction for each word....
It needs to be remembered that language usage changes over time. The source language (i.e., the original MSS) is a somewhat static thing (subject to ongoing textual criticism) of which we must make serious effort to understand in light of the culture and context of the original authors. This is where a Jewish perspective of the Scriptures is essential, for without this a lot of assumptions may be "read into" the original text and foreign ideas are used to convey what the translators think is an equivalent meaning for a target language/culture. That is why I always aim to understand how the original authors would have understood their own usage before looking at how someone else decided to render their findings in English.
The ideal thing is to study both Hebrew and Greek. Work hard to obtain a basic reading level (i.e., the ability to read the simpler constructions of the text and use orig. language dictionaries and grammatical tools). Then you can check the translation of a passage of interest and are no longer at the mercy of a translators. You can do some of your own investigative work and exegesis.
Why did the KJV translators use "Easter" rather than "Passover" for pascha in Acts 12? I really don't know, but I can say that it appears to be an anomaly of sorts: in general, the KJV stays close to the majority Greek text and gets it right far more often than wrong... However, the KJV (as well as nearly all English translations) still uses the word "Church," which I see as an even more serious problem, and there is just a "feel" to the reading (of nearly all the English translations) that is decidedly "Gentile" in perspective and outlook, esp. in the NT translations.
I hope that helps a little. Bottom line: Spare no effort to study the Scriptures in Hebrew and Greek (but especially the Hebrew, since its authority underlies the authority of the NT). Use the various translations as guides to help you understand the original writings. Pray and ask the Holy Spirit to give you wisdom and insight as you seek God's truth.