Welcome back! Lots of changes but not much you need to know in advance, you can just pick it up as you play again. Possibly start a new character or even new free account to do the tutorial and career agents to get you back into the general swing of things.
You can use Referral Links between your own accounts to give each of them 1,000,000 bonus SP.
Check the Returning Player Guide for some updates and tips.
If any of your assets are stuck in a hard to reach region (or the new Triglavian region of Pochven which was sort of yoinked out of high sec), you can check CCP’s guide to recovering assets:
Hope it all goes well for you, have fun!