Mobile RTS Naval game help please

hi guys im new to the forums my 1st time ever using the forums i hope this inst the wrong place to post, so basically i want to make a naval strategy/base builder game likes of Oceans and empires or Pirates of the Caribbean tides of war but obviously my idea of the game just using those 2 as a base for this post, im new to UE4 and working with maps at the moment i wanted to ask how to implement or where to start the idea of open ocean map and somewhere on the map the player would spawn in and build a base almost like a instance/ dungeon im not going to post the whole idea of the game lol as i would like to do 1 step at a time i have looked online / youtube but all the vidoes are for RTS more like turn based combat and land based games like war craft 3 ty you for your time.