At 26 you should find out what is causing this low T rather than jumping into TRT like that. Your doctor should know that before giving you cyp right away. If you don't have any insurance this will be expensive but I think worth it -- go see an endocrinologist. You might be able to get your own system up and running again with a restart or so. 26 years is pretty young to start pinning every week for the rest of your life.
To answer your questions:
1. 100mg is on the low side but I am a firm believer that 250mg is on the high side
2. You are not obligated to purchase what is on your script. I wouldn't tell your doc that you're going UGL tho.
3. You can up your dosage for a blast and come back to your TRT dose -- just make sure it's not around the time you visit your doc to check your bloods