I am amazed that someone has started with HoME!!!
But for the "novels" , if you want a true sequence it is hard to be exact but I would say that the basic sequence is Silmarillion Hobbit Lord of the Rings but the Children of Hurin is the fuller version of a story in the Silmarillion and Unfinished Tales has parts that relate to each so you might want to read that in parts - it has chapters that add to the stories of Tuor and Turin, then a lot more of Numenor that should be read with the Alkallabeth in the Silmarillion. The remainder should be read after LOTR (though the quest of Erebor chapter relates to the Hobbit it is the from the point of view of looking back after the events of the Lord of the Rings).
The letters are a delight and add extra insights but I think you will get more out of them after you have read all the main works.
. However since you have read LOTR you may also want to read the History of LOTR volumes of HoME.