The first thing you should do is, as you yourself point out, build satellites. The next one is to make workshops, and get as many engineers as possible (prefer missions where the reward is engineers above anything else), so that you can manufacture more satellites. This is really the only thing worth focusing in the first month. And keep in mind that if you slip too much on the high panic/low income slide, you won't be able to get back. Other momentary slips (like crappy interceptors = can't intercept all UFO's, crappy squad = can't finish difficult missions) you can recover when they hit you, but the panic/income is a one way street. That's why I think you should proritize satellites and workshops at the start (and really, for the better part of the game)
Other stuff like weapons, squad, interceptors, even research are good enough with their star-up allocations for the first month:
the squad is ok, their default weapons and equipment are fine. Maybe research S.C.O.P.E. and build one or two for your snipers, it gives you +10% accuracy and it's cheap enough to research & build. Other than that, investing in to fancier weapons/equipment in the first month will not bring any actual bonuses, and you will suffer from lack of satellites if you do that, and that equals lack of money and increased panic
the interceptors are really ok: they are tough enough to handle first-month UFOs. Maybe you can spread out a bit and add more interceptors once you raise a satellite over a previously unmonitored continent so that you can shoot down UFOs over there as well, but for the very first month you shouldn't buy more than 2 extra interceptors
research is fine, you'll dig into that later, once you have established a steady income. And, as with interceptors, investing a lot into research in the very first month can't really bring you much benefit.