It's pretty much impossible for us to tell you how likely you are to get addicted to drugs because we don't know you and there are many variables involved.
I will say this though- depending on how likely you "need" speed, I can see that becoming an addiction pretty easily. When drugs are used to get things done it's easy to become reliant on them for getting things done. Another significant risk of regular amphetamine use is neurotoxicity, which occurs every time you use regardless of addiction. Regular amphetamine use is really not safe.
Using opiates every three days is stepping into somewhat risky behavior in my opinion. I think that's getting to where it could be quite easy for you to slip into daily use. It only takes one binge to get you hooked.
I wouldn't worry about the weed, but then again, I smoke daily, so I don't worry about weed unless I'm running out, and even then I don't worry, I just pick up the phone. Still, daily weed use is generally not good for you. But in different and much less benign ways then daily amphetamine or opiate use.
Drug addiction is something you often don't really see coming, it can really sneak up on you, so be careful. It's easy to have a dosing schedule like you maintain and semi-accidentally slip into daily use.
If you're worried about it, and I agree that your schedule is perhaps risky, you should use less often. Keep amphetamine use to when you really need it (but not every time it would help), and opiate use to the weekends or less often.
