JR East Pass Tohoku

I'll be getting tohoku pass, here are my questions
-Do i need to make reservations for shinkansen? I.e. From tokyo to yamagata
-Can i purchase the pass online anytime? What is this 14-day validity?

You don't have to reserve seats, with a JR pass you can just go to the non reserved cars and find any free seat. Do note that a lot of the Tsubasa shinkansen split at Fukushima, half of the train going towards Morioka. You'll need to make sure you're in the right part of the train. If you reserve your seats, they'll know which section to seat you're in and you won't have to worry about this.

JR passes you usually can only purchase within three months of the start date of use. The 14 days means that from the date that you first nominate your pass to start, you will have 14 days to use the five days of JR train travel.

Thanks! I guess i'll just reserve our seats, it would be troublesome if we get on the wrong part of the train😂