For the Agility: Warrior with Speed Demon (2) gives +3 (4 with Narco) Agility.
Aaah, I forgot about custom drugs! I was in a Missions headspace, and they aren't allowed there. Makes sense, carry on!
ETA:
Man, Narco is so freakin broken...
So Warrior (STR+1, AGI+1, BOD +1, WIL -1) with Speed Demon 2 (AGI+2, REA +2, STR -1, INT -1) gives you AGI +4, BOD +2, REA +3, WIL -1, and INT -1? For 8R and 135¥ a pop that's just stupid good... See my comments about "too good to be true" earlier. I won't argue that it's not RAW, but compare that to other drugs like Cereprax or K-10 in terms of raw effects; those are crazy expensive, highly illegal, and have massive negative side-effects. In your case, you take 2S damage at the end of the 10 x 1D6 minute duration. Womp, womp.
Also, what's the addiction rating of that drug? I feel like I am missing something, as I don't see an explanation for the star in the table on page 192. I knew there was a reason we banned custom drugs at our table.
tl;dr: I like to play devil's advocate, please don't hit me with a rule book for being a rules lawyer. Regardless of what is RAW, GM decisions are final and I'm merely responding to questions asked. Again, please don't hit me with a rule book, I'm a gentle soul!
No really, feel free to ignore everything I say here.
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For diagnostics, I'd say that the bonuses from the Berwick Suit are roughly equivalent to the bonuses from a smartgun. Both are feeding you real time information to adjust your actions to a more desired result. Where I wouldn't stack is that the Berwick suit is one device and the Overcoat is a second device, which while technically true and their bonuses explicitly stack, I think is a cheese too far. Where this is limited is by the teamwork test (which in HighTimes case is 1), though there have been interpretation (that I don't agree with) that point out that Diagnostics is written differently than normal TW tests.
All said, I'd say that he's limited to 18 dice with sprites and and drugs (with the sprite(s) rolling well) on Automatics (SMGs), and 11 dice on social skills since he doesn't have more than 1 ability in any of them. Given that we've got a real face on the way, I'm not gonna worry about trying to squeeze any more juice outta the Social Skills. He can spend a lot of money and effort to not suck at them when needed
Addiction is a bitch, and I'm playing a junkie. That said, there's about a 75% chance of getting 3 hits on 11 dice. When you throw re-rolls for edge in there it jumps to >98% chance (if you allow edge for addiction tests). Again, with cheese, you could argue that you're *actively* using the nephritic screen to filter the drugs so could sprite the device (super SUPER cheese, and IMHO takes all of the risk of playing a junkie away).
End of the day, I get as many dice as you say I do when I do (and I mean that in the best way possible!) Negatives are negatives if the never cause a problem. HT is a junkie (probably with an attitude problem), and eventually the numbers are gonna catch up with him and he's gonna be *more* addicted.
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No worries man, it's all good. I get your point of view, I just happen to disagree
And absolutely, this is definitely one of those "GM call" moments. RAW is one thing, but RAW doesn't always make sense. And your example of Nephritic Screen is just off, by the way; that's bioware, so not an electronic device
On speedballing: 1) wish he could afford designer drugs! (well, he can on everything but the Cereprax, but ¥¥) 2) Do you have any effects other than those listed on p. 193 of Chrome Flesh for mixing? Also, would you say that Narco applies to the effects on that table (specifically the -2 damage and halving the duration)?
Oh, you haven't seen the overdose rules? Check SR5 page 415:
Too much of anything can hurt you, or even kill you. Whenever you take a substance while you’re already on that substance or one that has a shared effect (like the way cram and novacoke both affect Reaction), you take Stun damage with a DV equal to the sum of the Addiction Ratings of the overlapping drugs, resisted with Body + Willpower.
Essentially, take Psyche and Cereprax at the same time and you're looking at resisting (9+6)=15S DV with just body + willpower (ouch!). I would say that those rules are still in effect, as drug interactions from Chrome Flesh apply whenever you mix drugs. The core rules only apply whenever you mix drugs that have the same effects (i.e. both enhances Intuition, for example).
Finally, on acquiring things. I'd argue that a pharmacist doesn't have a very good CHA + NEG pool, thus by RAW would be almost impossible for them to get their hands on anything. But they sell drugs for a living, getting their hands on drugs is their *job*. Would they be able to sell me my drugs? Gotta say, that was kinda the story behind why HT would have a pharmacist for a contact. And he's got a, weak, background in chemistry. Either way lemme know. If we are going RAW, he's going to have a *really* hard time getting Cereprax (totally okay with that!) and we get to have fun with the withdrawls and such.
Sorry I rambled on so long 
That one would be up to the GM, but you could easily just take a Street Doc as a contact and call him or her a "pharmacist". Street Doc from SR5 has Negotiation 4 and Charisma 3, though, so not exactly a great guy for getting you stuff. I actually much prefer the Missions rules for contacts, as it means players don't have to build their own contacts according to some sort of unknown rule set, and one player ends up with vastly "better" contacts than another. So Dice Pool for Swag would be Connection + Connection + Loyalty, which if you have a highly connected pharmacist makes it a lot easier.
Hey keep in mind that as a newb I am well within my rights to do very stupid unrealistic things if I detect you using my newbishness to get superhigh die pools. I trust your judgement to use self control for roleplay sake and I can accomendate high die pools easily enough. I highly doubt none of you are gonna go without getting a glitch or crit glitch. But don't make me summon Deus. Im that crazy... of course your all nice people... right?
Hey, keep in mind there are other people on the team too! Just because our technomancer is high as a kite and rolls high dice pools doesn't mean the rest of us do; so if Deus shows up, please have him focus on the TM first
I'm sure it'll be fine; it's a cooperative game, and it's all about fun, right.
For what it's worth, I didn't figure you for a beginner either. But hey, we all had to start somewhere, so it's all good.
