Yes, you have to take the previous perks in the perk tree. Or at least the previous ones on the branch you are going up. Perks with multiple levels you only have to take 1 of to go further up the tree.
I think it is Non- Sequential in the terms that you have to be a certain skill with it, i dont think they would make you get every perk in the tree just to get to the higher ones if you have high enough skill i think you can just get it
I would be fine with taking the branches with 2 perks a level, but with only 1 perk a level its going to be very restricting. Gonna have to get a mod for it I guess.
The thing is some of the perks were already given to you for free in previous TES games once you reach 25 50 75 100 :mellow: so there's gotta be at least 2 perks per lvl to make up for it and the fact there is lots of good skills.