I've never added sun-dried tomatoes, but my two most popular herb-flavored fetas are Garlic & Dill and Herbs de Provence... everyone loves them, especially me, ha!
As for slimy feta brine, are you using a water-based brine? If so, add some calcium chloride to the water, otherwise the calcium leaks out of the feta and causes sliminess, if not completely dissolved. Not sure what the answer is if you're using a whey-based brine. :