Well I'm no pro so perhaps some of the vets could give you better advice. But IMO if you have been on Prop And Adrol for 6 weeks I think it is safe to say you have achieved some noticeable gains. And you have two options here.
A. Start your pct protocol and save the Sust-250 for a future cycle which you can start sooner rather than later if you PCT now.. Also it will be an easier recovery with a 6 week cycle than a 12+ cycle you will be running if you start the Sust.
B. Run Sust E3D till maybe week 10 or 12 however it's going to take some time to leave your system due to the longer esters in the Sust.
Also if you do decide to run it try spacing out what little prop you do have left between your Sust shots for the first two weeks to give some of the longer esters time to stabilize..
C. Yolo Sust-250 1 shot every week for the rest of your life!!! muahahahah
If it were me i'de pct and run Sust another time.. Or just another cycle in general once I were able to acquire ALL THE REQUIRED MATERIAL FOR A FULL CYCLE!!!