If you have little to no music theory training, you’ll want to start with Applied Professional Harmony™ 101 and 102. These books will teach you the basics, and combine harmony, songwriting and beginning orchestration/arranging instruction. The Scoring Stages™ #2 course is a good choice to study along with these books.
The Instant Composer:™ Counterpoint by Fux is recommended as the place to start with counterpoint. For more advanced study, take a look at The Serious Composer™ series of four republished classic works by Percy Goetschius that are considered “standards” in training many successful composers.