Almost all external keels develop a crack where the keel joins the hull. This is a really difficult place for any sealant or solution. For boat up north or those that come out of the water in the winter, the differential expansion rates of the keel and the hull start the crack. Sailing puts a lot of force on that joint and also causes the cracking.
Ask 5 different sailors about these cracks and what to do about them and you'll get 10 different answers from don't worry about it to you have to drop the keel and rebed the keel. Any solution should include checking the bolts to see they are properly torque. This has to be done when the boat is out of the water and sitting on its keel. As for any other fix, it is hard to tell by photos.
Dealing with rust will require grinding the rust off, priming with a metal primer and then several coats of epoxy barrier coat and then bottom paint. Depending on how extensive the rust is it can be done as a spot repair or take the whole keel to bare metal. If you do the latter, it will give you a chance to inspect the keel hull joint so you can narrow down those 10 solutions to just a handful.
On the keel, pick a paint company and follow their procedures from start to finish, don't take short cuts or you'll be back at it in a year or so. Also, try using a copper free bottom paint. The iron in the keel can react with the copper in the paint depending on the formulation. Copper free paints, like Petitt Eco are environmentally a better choice.