It depends if you plan on also doing the optional subscription, all the older content comes with ESO+ minus High Isles, you can play through those content while on the subscription which comes with 1650 crowns per month you are subbed. Once the sub ends, whichever individual content you like you can buy with crowns from the subscription. High Isles will also be purchasable that way the day Necrom releases.

However with the cost reduction so high, might as well get the full package.