For the legs, I wouldn't worry about it. Use it however you like. For the top I would worry about the cracks. That being said. It depends on what kind of work you are doing too. Are you going to make small boxes or a dinner table. Nice looking wood.
I'd place the underside up and use the holes for holdfasts or dogs.
Kevin, I agree with Adam. Also somewhere i seen a guy put "bowties" in the larger cracks, to prevent them from becoming larger. Then with some sort of resin with saw dust, of the same wood, he filled the other cracks. He planed the boards and the looked great. I believe the the repaired sides faced up. Ralph '
Thanks Paul, I actually have different wood for the top. I was all set to use the oak for the top, but after ripping the stock for the legs and stretchers, it's not a good choice. Some crack are deep and full of dirt, which does wonders for a new bandsaw blade. I have some maple from old church pews to laminate for the top. Keeping in the reclaimed theme.
Ralph, I'm familiar with using epoxy resin with fillers, sawdust to match, graphite or india ink to contrast. If I had a wide belt sander, that would be a possible cool solution. But I'm sticking to as few machines as possible, right now a bandsaw only. And I've sanded plenty of resin by hand while making a sailboat and will pass on that option this time around.
Good luck Kevin
I don't really think you'll have any problems either way really and it'll just boil down to aesthetics in the end. If you've got a pristine bench top, it might look a little odd with rustic legs but I'm sure it'll hold work just as well anyway.