Another thing that I strongly recommend is not building your entire shopping list from the outset, you'll be put off by just how long it is.
Do it in steps. Work a single suit up and a single gun. For practicality's sake, I'd say work on upgrading a maverick, with extra backpack capacity if you can swing it. Once you have that, future upgrades become a lot easier to gather materials for. Guns - a single weapon at G4-5, even a sidearm, will serve you better than a pile of guns at G3. Personally I recommend maxing out a tormentor and slapping both audio masking and noise suppression on it once you have the respective engineers unlocked. Even now when I'm running missions, that bad boy is pretty much my main gun. I hardly ever use my primary unless I'm on a massacre mission.