Yeah they're both important. Keep in mind that some people spend their entire lives studying this book. So there's only so much you can expect to absorb in one pass. I would say if you want to get the most out of your time, there are a couple things to keep in mind as you read.

In the old testament pay attention to what God wants from the Israelites and compare that to what people who claim to practice Judaism are doing today. Do they match up? Spoiler alert: no. There are also things in the OT that apply to the Christian church today (for example, things that are called an "abomination" back then are still bad today. Homosexuality, fornication, etc.)

For the new testament, we're looking at the modern church and people who claim to be Christians. The words of Jesus are the highest authority here. Do the actions of the church line up with what he told them to do?

For somebody that just wants to do a single sweep to be able to pick part dumb memes like this, using this framework as you read will help you pick out bits of information that are useful for anybody living in clown world.

As far as translation, KJV is the only one I trust. Jews hate it because it's the foundation of American tradition and morality. They've been trying to bury it with other translations for a while (the authors of the NIV admitted this). It can be tough to read at times because of the dated language, but nothing a dictionary can't fix. The 1828 Webster's Dictionary (webstersdictionary1828.com) has traditionally been trusted with this job. The KJV that you'll find at the bookstore is the 1789 version (it was originally published in 1611), so this dictionary is great for deciphering some of the tough words. It's rare that you'll have to do that though. For the most part KJV is in plain english. People like to meme about "thee" and "ye" but this is actually a useful feature that modern english has lost. The closest we have is "thee" meaning "you" and "ye" would be "y'all" (This chart (quora.com) might help). This helps make distinctions that modern translations lack. So it might be tempting to opt for a modern translation that's easier to read, but odds are that you'll run into a confusing conflict and end up going back to the KJV anyway.

Well this is getting long and probably more than you bargained for but hopefully it helps you get the most out of your time. It's not easy to read through the bible but there's good stuff in there that nobody teaches anymore.

All of it. You need to read the first to contextualize the second. If you read for like, half-an-hour per day, you'll get through the whole thing in a couple of months.