Good one IMO. Well, depends on the strain of the weed. Indica opens up the localhost and I get to explore a lot and introspect. Sativa's focus me on one thing and I roll my brain all around that thing's area and can produce a ton of code. Other uppers get me thinking about something in depth. Uppers and electronic music in a crowd at 3-4 AM get me focused more than anything.

That sort of question is highly personal. I've heard many, many people espousing the virtues of some strain of weed or other (eg claiming it helps you think and doesn't make you fall asleep so much) but I've never actually found one that doesn't primarily make me sleepy. I do have access to an enormous variety to try (and I've definitely done my due diligence, so to speak). This has led me to believe that for some people, some strains work differently than for others. This meshes well with my observation that everyone seems to have different recommendations.

Depends on the person, but for me combining them causes an important increase in anxiety, if you try cut in half the dose of both to be safe. Cannabis when coming down from amphetamines is a different story though.