where to begin?

Welcome to FABO! We'll need a bit more info to make any meaningful suggestions. Is your main objective to get it running and then restore it while you drive it or are you willing to pull it apart and do the whole restoration at once? I would start by deciding what kind of car you want when it's done. Show? race? daily driver? etc. Write down what the car needs to make it the way you want. Figure a budget! Start gathering the parts you need first and keep an eye out for things you will need later in case you find a good deal you can't pass up. If you're going to do a complete teardown and build it all at once, I'd start with the unibody and build subassemblies while the body is being restored. If you have to do the work while you keep it on the road, I'd make it reliable first, then plan the most serious work when you can take if off the road for the required time it will take. If you can buy replacement parts and assemblies to restore, it will save on down time. Once you get, say, another K-member with the suspension/steering all done, It would only be a days work to swap it all out and you would be able to drive it the next day. That's a good way to do upgrades too. Get all the parts together, restore them, and then do the installation.