Apart from maybe the last one, none of them are classical algo problems.

They're basic math problems.

Query takes N milliseconds which is too long, mainly consisting of z & c when I run my profiler. It does x * y = z of these things and a * b = c of these things.

As z is the biggest number, can I reduce x or y?

Basic maths.

And even the last one you're better off actually trying out the technologies to trying to armchair theorize which tech is a better fit as without reading all their code you can't really see what they're really doing compared to what they say they do. Heroku being a pertinent case in point.