I never played the first one. you get all the backstory in the second. I don't feel like I missed anything but eventually I'll go play the first. Maybe if they put it in the engine for 2 because the first looks like crap.

If you really like lore, sure. It's not necessary. I think the second one is way more polished. I bounced off the first one pretty hard, but I'm still enjoying the 2nd.

Don't have to but highly advised to do so. It will contextualise significant parts of the background and character histories. The first one is also a masterpiece, so you should try it out and see if the game type is your cup of tea, with the benefit of a lower upfront investment. If you like it, when you're done with it, the second one may even be cheaper at the time and you get some more of that warhorse goodness.