Does this game have i-frames like Souls? Can I roll through attacks?
IFrames are much smaller here than in Souls. You can still abuse them but you have to be more precise. It's been a while since I played it and I may be misremembering, but I think it works like this:
In low and mid stance, your dodge is a quick step with a very fast animation but very few iframes, more suitable for getting out of the way quickly than phasing through damage hitboxes. I think if your gear weight goes over some threshold it turns into a roll animation. The roll is slower but has more iframes.
In high stance, the dodge is always a roll.
If you are light enough to do quicksteps, pressing dodge right after a quickstep will make you roll right after quickstepping, which greatly increases the range of your dodge + you get the bonus iframes from the roll.
Generally, the hitboxes in this game are precise enough to where if you are good at quickstepping you can move out of enemy attacks. There are exceptions, like command grabs, which do that bullshit thing where your character sometimes gets rubberbanded back into the enemy's grab animation even though you clearly dodged it.
Also, blocking in this game is very very important, much more so than in Souls. As long as you have enough stamina, you can completely block damage from physical attacks and partially block elemental attacks. Don't get stuck in the "i'm only gonna roll" mentality and start blocking more and you will be amazed how many attacks you can easily get out of unscathed.
Hope that helps.
Nioh games have a higher skill floor than Souls games, there are more mechanics and shit to learn. Don't get discouraged, usually if you take the time to learn by mid game you will be stunlocking enemies to death with 30 hit combos while perfectly weaving through theirs.