Surfing Waves

So I just got this board and it has a bunch of cracks. I'm most concerned about the first three as they go pretty much to the foam from what I can tell. Do I have to completely repair these (as in cut out the cracked stuff and replace it with some fiberglass cloth) or so you think I can just sand and then coat over all of them with fiberglass resin?

There are many ways to fix a board. If you leave behind fiberglass that is detached and don't get resin underneath it to stabilize it then that will be a weak point likely to break easily. There is microfiber filler that you can mix in resin or you buy it with the stuff already added which will make a resin repair a little stronger but not as good as fiberglass cloth. I think all of these could be repaired without fiberglass cloth but for the ones that go through the glass it will be a weak spot so if you are lazy use the chopped up fiberglass or microfiber mixture resin for those. But watch closely because if it gets whacked there again it will need to be repaired again. Be careful about the type of resin compared to the type of foam.

1- need fiberglass
2- sand down to fiberglass layer and just resin
3- same
4- same
5- lightly scuff up and resin

But if you haven't work with cloth before, I would get Solarez that has chopped fiberglass in the gel and goes off in UV light ( for all except #5 ).
Way easier, cheaper and less mess.