Question 18-Day Scotland Itinerary by Train and Bus

Hello!! I am a first-time poster and it’s my first time to the UK. I will be traveling by train and bus for 18 days in Scotland, and I’m trying to craft the perfect itinerary. I want to explore both the cities and the countryside, hitting places like Edinburgh, the Highlands, and maybe the Isle of Skye. Any suggestions on must-see spots, travel tips, or how to efficiently use public transportation? Also, are there any hidden gems that I shouldn't miss? Thanks in advance for any help!